Hybrid imaging method to monitor medical device delivery and patient support for use in the method

ABSTRACT

This invention discloses a method and apparatus to deliver medical devices to targeted locations within human tissues using imaging data. The method enables the target location to be obtained from one imaging system, followed by the use of a second imaging system to verify the final position of the device. In particular, the invention discloses a method based on the initial identification of tissue targets using MR imaging, followed by the use of ultrasound imaging to verify and monitor accurate needle positioning. The invention can be used for acquiring biopsy samples to determine the grade and stage of cancer in various tissues including the brain, breast, abdomen, spine, liver, and kidney. The method is also useful for delivery of markers to a specific site to facilitate surgical removal of diseased tissue, or for the targeted delivery of applicators that destroy diseased tissues in-situ.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the field of medical imaging and particularlyto a hybrid imaging method and apparatus used to monitor and optimizethe placement of interventional medical devices in human tissues.

2. Background of the Art

A number of techniques, methodologies, apparatus and systems have beenproposed to improve the accuracy of instrumentality placement such asneedle or catheter placement into tissue based on measurements from 3Dimaging formats. These imaging formats (such as Magnetic ResonanceImaging, sonographs (ultrasound), fluoroscopy, X-ray, and the like)locate the needle entry device in relation to treatment- ortherapy-targeted tissue, such as MR-detected target tissue. Theseimaging formats generate imaging data that are used to determine theappropriate positioning of the needle during treatment, which needletypically is placed in a guide device and moved into the tissue. In manycases, the needle is delivered solely on the basis of this imaging datainformation and confirmation of the final needle position relative tothe target requires a second set of images to be acquired. In caseswhere tissue stiffness variations are extreme, the needle may deviatefrom the desired path and deflect on-route to the target tissue.Similarly, the needle may distort the tissue itself and thereby move thetarget tissue to a new location, such that the original targetingcoordinates are no longer correct. Further limitations of currentsystems include the fact that needle position is often determined byreference to its artifact generated in the MR images. From thisartifact, the operator infers the actual needle position relative to thetarget position. In many situations this is appropriate; however, whentargeting small lesions (i.e. <7 mm), the needle artifact (often 5-9 mm)may obscure the target, limiting the ability to use even real-timeimaging data, as from MRI, to validate needle/target position.

Numerous articles have been published in the medical literaturedescribing imaging methods which can be used to monitor and optimize theplacement of interventional medical devices in human tissues (e.g.,Greenman et al, Magnetic Resonance in Medicine, vol. 39:108-115, 1998;Orel et al., Radiology. vol. 193, pp. 97-102, 1994; Kuhl et al.,Radiology. vol. 204, pp. 667-675, 1997; Fischer et al., Radiology, vol.192, pp. 272-272, 1994; Doler et al., Radiology, vol. 200, pp.863-864,1996; Fischer et al., Radiology, vol. 195, pp. 533-538, 1995; Daniel etal., Radiology, vol. 207, pp. 455-46, 1998; Heywang-Kobrunner et al.,European Radiology, vol. 9, pp. 1656-1665, 1999; Liney et al., Journalof Magnetic Resonance Imaging, vol. 12, pp. 984-990, 2000; Schneider etal., Journal of Magnetic Resonance Imaging, vol. 14, pp. 243-253, 2001;Sittek et al., Der Radiologe, vol. 37, no. 9, pp 685-691, 1999; Jolesz,Journal of Magnetic Resonance Imaging, vol. 8, pp. 3-6, 1998; Lufkin etal., Radiology, vol. 197, pp. 16-18, 1995; Silverman et al., Radiology,vol. 197, pp. 175-181, 1995; Kaiser et al., Investigative Radiology, vol35, no. 8, pp. 513-519, 2000; Tsekos et al., Proceedings of the IEEE 2ndInternational Symposium on Bioinformatics and Bioengineering Conference,2001, pp. 201-208).

To address limitations described in the published prior art, a means toverify the actual trajectory of the needle is needed. A satisfactorymethod must be capable of observing the target tissue to ensure eitherthat needle deflection or target tissue movements can be incorporatedinto the needle delivery path, thereby ensuring accurate needledelivery. Modified bore design MR magnet systems have been developed toprovide more open access to the patient. As such, imaging and needlemanipulation can take place concurrently with the physician having someaccess to the patient while the patient is positioned in the bore.However, these “open” systems are not always available and are often ofsuboptimal field strength, which can result in reduced image quality.Other proposed solutions in the art involve in-bore robotic devices thatenable manipulation of the needle within the bore of the imaging magnet.While this approach usefully addresses the issues of tissue/needledeflection, it also removes the normally close interaction between theradiologist and patient, which may lead to high levels of patientanxiety.

SUMMARY OF THE INVENTION

The present technology provides a medical imaging system capable ofvarious imaging and interventional tasks based on non-invasivedetection, such as MR-detection, of diseased tissue, with many of theseapplications utilizing a hybrid imaging approach in combination withultrasound imaging techniques. The apparatus and techniques disclosedare combined in a system capable of various imaging and interventionalstrategies that can be utilized for comprehensive treatment protocols,for example, complete breast cancer management. Typically, the devicesare delivered through thin needles (ranging from 20 to 9 gauge sizes(0.81 mm—2.91 mm)) which may either place devices into the tissue orretrieve tissue from a specific anatomical region.

The present technology uses 3D imaging data obtained by conventionalnon-invasive imaging techniques, particularly MRI (magnetic resonanceimaging), US (ultrasound), positron emission tomography (PET),computerized tomography (CT), or other three-dimensional imaging system.The technology discloses a number of imaging and interventionalfunctions required for complete breast-MRI patient management, includingscreening for breast cancer, determination of tumor extent andmulti-focality of previously diagnosed cancer, and diagnosis ofsuspicious lesions. Further applications of the technology includeMR-guided positioning of wires and marking devices in the breast tofacilitate any treatment or diagnostic procedure, such as thoseincluding but not limited to surgical excision/biopsy, MR-guided corebiopsy for lesion diagnosis without surgery, and MR-guided and monitoredminimally invasive therapy to destroy diseased tissue. Multi-modalityMR/US breast imaging disclosed in the descriptions of the presenttechnology enables a more effective means of interventional devicepositioning (more accurate, faster, less invasive to the patient), ameans of tissue diagnosis without biopsy (through ultrasound (referredto herein as “US examination”), and a means of monitoring tissueablation boundaries when performing minimally invasive therapies.

While the method of the present technology was specifically optimizedfor breast cancer management, it will be understood by those of ordinaryskill in the art that the techniques and apparatus of this technologycan be easily adapted to various other body parts and pathologies.

One aspect of the present technology is to provide a patient physicalsupport system, including patient support and transport stretcher thatis designed in such a manner to enable maximum access to one or bothbreasts by the operator.

A second aspect of this technology is to provide a compression systemwith four or more independently movable plates designed to avoidinterference with US examination transducer and biopsy needle delivery.

“Four or more” may limit bilateral-only implementations

A third aspect of the present technology is to provide a transportstretcher or gurney to aid patient access to the interventional area,the apparatus to include a bridged interventional gap, IV (intravenous)poles which accompany the patient during the entire procedure, aheadrest which accommodates the patient's arms and permits a view out ofthe magnet, and mirrors and lighting to help better position thepatient.

A fourth aspect of this technology is to provide breast compressionplates with various apertures and fixtures to accommodate various MRimaging coils or other radio frequency devices, USexamination-transparent imaging plates, device guide plugs with straightor/and angled orientations, a goniometer system for needle positioning,US examination transducer positioning system, and freehand transducercalibration system.

A fifth aspect of the present technology is to provide software tocalculate needle trajectory based on fixed fiducial positions, to enablemultiple targeting, and to determine a shortest distance to lesion.

A sixth aspect of this technology is to provide additional software tocalculate angled needle trajectory based on fixed fiducial positions, toenable multiple targeting through multiple incisions, to enable multipletargeting though a single incision, to determine a shortest distance tolesion, and to determine any potential interference of needle handlewith surrounding apparatus.

A seventh aspect of the present technology is to provide software for USexamination transducer delivery based on fixed fiducial positions, toenable multiple targeting, to determine shortest imaging distances tolesion, to recalculate with transducer in two orientations, torecalculate with transducer at various angulated orientations, and toconvert tracked transducer coordinates to corresponding stereotacticframe coordinates.

An eighth aspect of the present technology is to provide stilladditional software to convert MR-data,set scan plane and distance totarget.

A ninth aspect of this technology is to provide additional software forvarious MR/US image co-registration, visualization, and image processingtasks

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a shows the stretcher and patient support attached to the MRimaging system according to the invention; b is a side-view of thestretcher with patient in the ‘arms back’ position.

FIG. 2 a shows the patient support structure without sternum orcontralateral breast support. b shows the support structure withattached breast constraint and sternum support, which is angled so as toprovide good medial access to the breast. c and d show the ability toaccess various positions in the breast with various interventional probeorientations with respect to the patient support structure andcompression plates.

FIG. 3 shows the extra interventional volume provided by an opening inthe stretcher according to the invention. a shows one aspect in whichthe member bridging the opening may fold down into the volume. b showsanother aspect in which the member may roll under the patient support inthe stretcher. c shows that the member may also break into multiplesections that may swing laterally and out of the way. d shows anotheraspect in which a portion of the patient support member may lower toprovide an accessible volume. e shows another aspect in which the frontand rear sections of the patient support raise in order to provide anaccessible volume. f shows another aspect in which a slim support with agap smaller than the support wheelbase distance ensures one wheel on thehead end of the apparatus is always in contact. g Shows another aspectin which a bridge support that may move either to the right or left sideallowing medial access to the breast while ensuring the wheels are incontact with the stretcher support surface h Alternatively, sections ofthe stretcher may be removed to permit increased access to the breast.

FIG. 4 shows how the patient support structure may be cantilevered overthe interventional volume according to the method of the invention. Thisdesign provides for the maximum access to the breast. b shows the shapeof the arches relative to the MR bore. In order to prevent the structurefrom tipping over with a patient in place and separation of the patientsupport from the stretcher, sliding or rolling constraints can beincorporated into the system. c shows various embodiments of theseconstraints. d shows the extension of the arch support structures sothat they form a complete cylinder around the patient.

FIG. 5 shows the plate locking/positioning system of the patient supportand the related apparatus according to the invention. The compressionplates can be moved anterior/posterior within the plate locking support.a illustrates how the compression plates/locking supports can beintroduced from the side of the apparatus. Each plate can be movedindependently and to any position in the left/right direction. b showsthat additional compression plates in the superior/inferior directioncan be accommodated so as to “box” the breast. c shows another aspect ofthe invention whereby various embodiments of rail positions are possibleas well as flexible sling designs to compress the breast against thechest wall.

FIG. 6: illustrates how various compression plate designs may beaccommodated according to the invention. a Attached to the compressionplate are fiducial markers and fixed positions to attach coils andpositioning stages. b Attached to these compression plates (or embeddedwithin) are sets of coils. c The compression plate may be a fenestratedplate for needle access. d The plate may provide an acoustical openingfor US imaging and intervention. e A transducer positioning stage may beattached at a fixed position on any compression plates.

FIG. 7: shows various coil configurations that may be used according tothe invention. a Bilateral imaging application with 4 coil array. bUnilateral imaging configuration with 4 coil array. c Bilateral imagingwith 4 coil array. In order to minimize the interaction between themedial coils, their size has been reduced (size reduction is not aclaim, so should not be spelled out?) and one or more RF devices whichoperate to decouple the medial coils is introduced. These can beattached to sternum support or positioned by attaching to the platelocking/positioning system as shown in d. and e Additional coils may beincorporated at other positions such as within an anterior/posteriorcompression plate, or within the patient support structure.

FIG. 8: shows various interventional compression plates that may be usedaccording to the invention. Different fenestration shapes can beimplemented as illustrated. A unique feature is the addition of a notchto one side of the opening or indexing component to make it asymmetric.This ensures plugs may be positioned into the opening in only oneorientation. A compression plate consisting of a sterile membrane pulledtaut across the frame as illustrated can be used to compress the breastas well can enable needle entry after making a small incision in thesurface.

FIG. 9 illustrates systems for breast biopsy disclosed in the prior artwhich are based on a pair of parallel compression plates to immobilizethe breast and provide means to direct a needle to a lesion based onfiducial marker measurements made in the MR image.

FIG. 10 a shows how a needle holder may be used according to theinvention to allow arbitrary orientations of a needle for biopsy. Afterthe correct orientation is achieved, the gimbal is locked in position bytightening the threaded clamp. By reducing the dimension of the gimbalas illustrated in b the point of rotation is positioned near the skinsurface.

FIG. 11 illustrates some useful aspects of needle orientation geometryaccording to the invention.

FIG. 12 shows a goniometer that may be used according to the inventionto define needle guide orientation.

FIG. 13 illustrates the angulated biopsy procedure according to theinvention.

FIG. 14 shows a combination fenestrated plate and compression membrane.According to the invention, by compressing the breast using acompression membrane with a fenestrated plate that can move relative tothe breast, more of the breast is accessible for needle guidance.

FIG. 15 illustrates the MR-Guided delivery of tumor boundary markingclips according to the invention

FIG. 16 illustrates the MR/US co-registration procedure which can beused according to the invention. The lesion and fiducial markers areidentified using MRI. Based on the MRI information, an US transducer isdelivered to the appropriate position so that the lesion is centered inthe US image using a stereotactic frame.

FIG. 17 illustrates the MR/US co-registration procedure where afree-hand US transducer positioning system may be used . A touch pointis used to register the coordinate system of the tracking device to thefiducial marker defined, and therefore to the MR image's coordinatesystem.

FIG. 18 shows different US probe delivery techniques which can be usedaccording to the invention. Using a mechanical stage with 5 degrees offreedom, capable of fixing an US probe horizontally or on edge, allowsaccurate transducer positioning. Important features enable imaging nearthe chest wall (i.e. apparatus and structure do not encumber access tothis region). a shows a frame with open central aperture and embeddedfiducial markers that may be inserted into the compression frame toprovide touch point reference to co-register the tracking system to theimages.

FIG. 19 illustrates some useful features of the US transparentcompression frame according to the present invention. The thin, angledtop support member helps support the patient and the U-shaped supportframe enables full US imaging access to the breast. b, c and d showalternative embodiments of the US permeable membrane with many cut awayopenings.

FIG. 20 shows various MR/US Hybrid biopsy configurations according tothe invention. a shows the breast compressed between two sterile, UStransparent plates. Imaging and intervention occur from the same side. bshows a configuration with one fenestrated plate and one US permeableplate. The needle approaches from the opposite side from US imaging. cshows a plate with larger fenestrations that can be used to introduce atransducer and needle for same-sided imaging and intervention. d showstransducer and needle delivery through the same side using a positioningstage.

FIG. 21 Illustrates various MR/US Hybrid biopsy configurations accordingto the invention. a shows the breast compressed between two sterile, USpermeable plates. Imaging and intervention occur from the same side witha medial approach b illustrates a configuration with one fenestratedplate and one US permeable plate. Needle approach selected opposite sidefrom US imaging. c shows a plate with larger fenestrations that can beused to incorporate a transducer and needle for same-side imaging andintervention. d shows an embodiment with 2 point needle positioningsystem on opposite side to US imaging.

FIG. 22 Shows hybrid device guidance for delivering multiple markers inthe breast to demarcate tumor boundaries using various compression plateconfigurations. According to the invention, this can be performed in ananalogous manner to MR-guided marker placement.

FIG. 23: Hybrid needle guidance for positioning of multiple markers inthe breast to define tumor boundaries demonstrated from the physicianspoint-of-view.

FIG. 24 a According to the invention, hybrid needle guidance can be usedto position tissue ablation probes and monitor therapy progression. Inthis example, a cryoablation probe can be positioned to the center ofthe lesion using hybrid guidance. b shows how reformatted MR images maybe used to define the tumor extent, while US may be used to monitor icethe development of the resultant ice ball.

FIG. 25. Flowchart illustrating the MRI-guided needle localizationprocedure according to the invention.

FIG. 26. Flowchart illustrating the MRI-guided core biopsy procedureaccording to the invention.

FIG. 27. Flowchart illustrating another embodiment of the MRI-guidedcore biopsy procedure according to the invention.

FIG. 28. Flowchart illustrating the hybrid MR/US imaging procedureaccording to the invention.

FIG. 29. Flowchart illustrating the hybrid-guided core The foregoingfeatures, objects and advantages of the present invention will beapparent to one generally skilled in the art upon consideration of thefollowing detailed description of the invention.

FIG. 30. Flowchart illustrating the hybrid-guided marker placementprocedure according to the invention.

FIG. 31. Flowchart illustrating the hybrid-guided delivery of tissueablation probes and monitoring of therapy according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following described technology encompasses a hybrid imaging methodto monitor the placement of interventional medical devices and apparatusthat can be used in such an imaging method and other medical ortherapeutic procedures. The preferred embodiments are described byreference to both the general and specific attributes and features ofthe components of the technology. However, this specification disclosesonly some specific embodiments as examples of the present technology,which as not intended to be limiting in the interpretation of the scopeof the claimed invention of this Patent. It will be readily apparentthat variations and modifications may be effected without departing fromthe true spirit and scope of the novel concepts of the invention.

Patient Support and Transport Stretcher

One of the areas of disclosure of this technology is a patient supportapparatus such as a structure, gurney or stretcher 1 as indicated inFIG. 1. This patient stretcher 1 and table top support apparatus 2 actto support the patient 26 and to immobilize the breasts 36, providing atransportation system for carrying the patient 26 into the MR imagingmagnet system 4, as well as providing a stretcher 1 and support 2 forthe patient during imaging which can be attached and detached from theMR imaging system 4 and moved to other locations. The patient 26 lies onthe apparatus 2 in the prone position (face downward) and may beadvanced feet first into the bore 24 of the MR imager or magnet 4. Thepatient's breasts 36 fall into an opening 19 at the chest level of theapparatus 2 and then can be immobilized by compression plates (not shownin this FIG.) in a medial-lateral direction. According to the technologydescribed herein, the patient support section of the apparatus 2 hasbeen designed to: 1) provide room for large breasts to extend into tothe access volume without touching the bottom of the magnet bore, 2)optimize room available for the patient in the magnet bore, 3) allow thepatient's arms to be positioned forward above their head or at theirsides, 4) provide access both medially and laterally to either breast,particularly towards the chest wall, 5) ensure devices with a wideranges of oblique orientations have maximal access to all points withinthe breast, all with optimization for patient comfort. The design of thesystem of the present technology thus serves a multitude of imaging andintervention functions, with very little adjustment of the components.Medial and lateral interventions and hybrid imaging interventions can beaccomplished without prior knowledge of the approach required. Theapparatus disclosed by the present invention is substantially differentfrom systems currently available commercially, such as, for example, theequipment made by MRI Devices, and USA Instruments. Systems presented bySu (U.S. Pat. No. 6,163,717), Liney et al, “Bilateral Open Breast Coiland Compatible Intervention Device,” Journal of Magnetic ResonanceImaging, 2000 are dual function breast imaging and intervention systems.These systems lay on the MRI bed with no modification to the normalstretcher's table top. As space is limited in an MRI magnet bore, theunmodified tabletop limits to space available for access to the breastand for the patient in the magnet. None of these systems are used forfunctions other than MR imaging or MRI-only interventions and requiresignificant setup time in the MR imaging magnet to convert from an MRimaging to MR interventional system.

The concept of a specially designed patient support system and stretcheris not believed to have been presented in the prior art. Schneider etal, 2001, presented a modified MR stretcher for the purpose of MRIbreast biopsy. This invention was also presented in U.S. Pat. No.5,855,554. The top support surface was modified to enable more access tothe breast, whereas the bottom part of the stretcher was not modified.Breast biopsy systems presented by S. H. Heywang-Kobrunner, 1999, Kuhl1999, Fischer (U.S. Pat. No. 5,913,863), Cardwell (U.S. Pat. No.6,423,076) all present modifications to the top surface as well, with nomodification made to the stretcher component. These systems compromiseMR imaging capability for improved access to the breast. No integratedsystem has been developed in an attempt to maximize access to the breastby modification of the tabletop and stretcher, and providing provisionsto use the system for imaging, intervention and multiple modalityfunctions. These concepts can be easily transferred to embodimentswherein the stretcher is a non-wheeled structure, or a stationarystructure.

As shown further in FIGS. 1 a, 1 b and FIGS. 2 a) and b), in anexemplary embodiment of the technology described herein, the patientsupport 2 consists of a winged structure with no medial or centralstructural members. There is a cervical (shoulders, neck and head)support area 6. The two arches 28 connect the head support 18 and armsupport 25 (cervical section) to the lower patient support 27 (lumbar orthoracic section). These arches 28 are positioned posterior to thepatient's breasts so as to maximize access to the patient's breasts in alateral approach. These arches 28 further provide a restraint for thepatient's arms when they prefer to have their arms at their sides.Another feature of these arches 28 is to ensure a strong structuraljoint between the superior and inferior portions of the patient support.The arches can be made as large as needed to ensure the requiredstrength and introducing a curved geometry to the arches ensures thatthe arches can be introduced into the MR imaging bore. In the extreme,these arches 28 could form a complete cylinder in which the patientwould be placed to maximize the strength of the patient support. Doublearch supports have not been presented as a means to provide thefundamental support or connectively between the cervical and thoracicsections of the apparatus.

The general shape of the patient support 2 is such that it may rampupward (inferior to superior) towards the opening for positioning of thebreasts, and then may tend to slope downward away from the openingtowards the head support 18. The inferior ramp 27 positions the patient(not shown) so that her pendulant breasts will not touch the floor ofthe magnet, providing a large volume for interventional access. Thesuperior ramp 29 (if present) provides a region for the patient's armsto rest when in the arms-forward position (arms above the head). The useof arching members as the primary structural component to the system,with or without a removable sternum support is unique. The geometrypresented in FIG. 4, has been designed to provide structural support andpatient support so as not to interfere with access to the breast.

The volume available for interventional access is maximized by thetransport stretcher and the design of the table structure to provide anangulated entry geometry to the lateral aspect of the breast volume butcreating wide or tapered entry of the table structure toward the patientvolume from the lateral aspects. The access provided by this arch designis illustrated in FIGS. 2 a) b), c) d). A bridge section 8 of thetransport stretcher 1 provides support when the patient support is beingrolled into the magnet bore, but is designed to retract out of the waywhen the patient support is fully removed from the magnet forintervention, as illustrated in FIG. 1. In one embodiment of thistechnology, a headrest 18 is situated at the superior end of the patientsupport, whose height and angle may be adjusted (FIG. 2 c). Mirrors 40may be provided below the headrest 18 to allow the patient aright-side-up view out the front of the magnet. This feature of thetechnology is intended to reduce patient anxiety. The embodiment shownhas a single telescoping headrest support 18 which incorporates thetilting adjustment to maximize the room available at the superior end ofthe structure, and to permit adjustment and clamping of the headrestorientation with one hand. A simplistic headrest design has beenpresented by Schneider et al, 1999, however this design does not embodyany additional features described above.

In further embodiments of the technology described herein, bridgemembers may be used to support the patient over the breast accessvolume, as shown in FIGS. 2 a, b), c) and d). For applications involvingboth breasts (bilateral applications) a sternum support member (44 asshown in FIG. 2 b)) may be used. For unilateral applications, a bridgemember that supports the contralateral breast and compresses it againstthe chest wall is attached. Unlike the device described byHeywang-Kobrunner et al., “MR-Guided percutaneous excisional andincisional biopsy,” European Radiology, vol. 9, pp. 1656-1665, 1999, inthe present technology, the angle of this support optimizes medialaccess to the breast while supporting the patient in a comfortableposition. Angulation of this member 34 (10-30 degrees) further providesimproved access to the breast for medial access with an angulated deviceapproach. The embodiment of removable sternum and contralateral breastsupport so as to maximize access to the breast from medial and lateralaspects as presented is unique with respect to the prior art. Removal ofthe breast and sternum supports are indicated in FIGS. 2 a) and b). Thisresulting improved angulation is demonstrated in FIG. 2 c) with theneedle approaching the breast beneath the contralateral breast support.Maintaining the sternum support in place would result in a limitedangular access to the breast. Schneider et al, 2001 (E. Schneider, K. W.Rohling, M. D. Schnall, R. O. Giaquito, E. A. Morris, and D. Ballon, “AnApparatus for MR-Guided Breast Lesion Localization and Core Biopsy:Design and Preliminary Results,” Journal of Magnetic Resonance Imaging,vol. 14, pp. 243-253, 2001) shows the top portion of the tabletop couldbe rotated to accommodate either left breast or right breast access. Noattempt was made to improve access to the breast for imaging orinterventional procedures as is provided by the system presented in thisdocument by way of a unique tabletop structural support and optionallyremovable sternum and contralateral breast supports.

Another feature demonstrated in FIG. 2 b and FIG. 2 d is the addition ofa disposable blood barrier 42 that is attached to the patient supportstructure. Features at the base of the thorax (thoracic) support 33 andthe shoulder and neck (cervical) support 31 allow attachment of variousblood catchments (plastic diapers). These can be easily attached andremoved during the procedures. A further preferred embodiment shown inFIGS. 2 a and b consists of IV poles 22 at the inferior and superiorends of the apparatus. This pole acts to hold the saline drip during thebreast procedures. No attempts have been made to implement any of theseembodiments in the prior art.

FIGS. 2 c and d shows a patient support structure with respect tointerventional and imaging probe access. FIG. 2 c (Front View) showsInterventional or imaging probes 30 may be introduced at variousorientations to the breast from either medial or lateral directions.(Note: only a portion of the patient support structure 2 and compressionplates 32 are shown in this view). Arrows indicate range of probe 30positioning without interfering with apparatus infrastructure. FIG. 2 d(Lateral view): Varied access of probes 30 is shown in a side view.Tapered geometry of patient bed (not shown) and positioning ofcompression plate 32 locking mechanisms and rail guides (not shown) farfrom a breast enables large angular and positional access. This taperedgeometry extends to the medial aspect through a gradually slopedcontra-lateral breast support 34.

Transport Stretcher

The transport stretcher 1 is used to transport the patient to and fromthe MR imager, to advance the patient into the magnet's bore, and as atable for the patient support during interventional procedures and USexams, which are performed away from the MR magnet's field (FIG. 1). Thepatient support 50 (e.g., FIG. 2 a)) rolls on the guides of thetransport stretcher when advancing into the guides 23 in the bore. Onthe underside of the patient support are a set of wheels and across-section corresponding to the internal geometry of the bore of themagnet. The transport stretcher attaches (docks) to the connectionmechanisms of the imaging system. The interlocks and safety mechanismsdepend on the specific design of the magnet. In order to have completeaccess to the breast when the patient and patient support, are removedfrom the magnet bore, a large section of the stretcher can be retracted(FIGS. 3 a-d). In the method of this technology, this can beaccomplished in a variety of ways as illustrated in FIGS. 3 a-d). Thevolume must be accessed in such a way that the patient support componentwill continue to be supported across this gap and not be in a fullcantilever position at any time (i.e., wheels on patient support willalways be in contact with a surface on the stretcher or MRI bore whenmoving in or out of the bore). In order for this to be accomplished,there are a variety of embodiments. 1) A member (e.g., 56) that folds upfrom either the torso, or the head end of the stretcher. 2) A member(e.g., 72) that pulls out from under the torso end of the stretcher, 3)Two members (e.g., 68) that split apart and hinge out laterally. The gap57 in the structure provides additional interventional volume.Additional embodiments may also include side walls 58 that match thegeometry of the magnet. This provides the operator with a means ofverification that needles extending from the breast will not hit theside of the magnet as the patient is returned into the magnet for anyadditional MRI scanning. As the large interventional access area isunique to this invention, mechanical provisions to enable use of thisadditional space without compromising patient safety, or complexity forthe operator as presented in this document are unique with respect tothe prior art.

Additional features of the stretcher may include a set of drawers in theside to organize all the secondary apparatus associated with the system.Further embodiments of this technology may include a set of lights 60 onthe medial/lateral faces of the right and left sides of the breastand atthe bottom of the gap in the stretcher. The orientations and intensitiesof these lights may be adjusted by the technician or radiologist.Another embodiment may be an adjustable mirror 62, or a mirrorpositioned on the lower part of the apparatus that allows theradiologist to more easily see the position of the nipple when thebreast is compressed. This is a desirable feature in the method of thetechnology described herein, because the nipple is often used as animaging landmark in the breast, and uneven compression may cause it todeviate either medially or laterally, thereby providing an unreliablelandmark. These features of the present invention are shown in FIGS. 3a-d.

In FIG. 3 d, the stretcher is shown with the telescoping bridge 64 beingelevated into support position.

FIG. 3 e shows that the entire stretcher, with the exception of thebridging 65 can be raised or lowered to provide a flat surface whenadvancing the patient support into the bore or to provide a gapfacilitating device delivery and intervention.

FIG. 3 f shows that the stretcher may have a slim support 66 with a gapsmaller than the support wheelbase distance, which ensures one wheel onthe head end of the patient support is always supported

FIG. 3 g shows a stretcher with a bridge 69 that moves left or rightallow medial access to one or the other breast.

FIG. 3 h shows a patient stretcher with a removable section 70 and thearea from which it has been removed 71. This allows medial access to thebreasts while assuring that the patient support structure 2 is incontact with the stretcher support surface 1.

Another embodiment of the technology is a stretcher which providespatient support in a full cantilever position based on stronger archedmembers, adjusting the mass distribution of the apparatus to move thecenter of mass towards the inferior end of the bed and the addition ofsliding or rolling constraints in the transport stretcher and magnetbore as needed to ensure the patient support cannot tip from thetransport stretcher during patient manipulation FIGS. 4 a, b, c and d.An example of appropriate tabletop constraints are illustrated in FIGS.4 a, b, c and d. In the context of a cantilevered design, the shape ofthe patient support 2 and the arches 28 ensure rigidity of the supportand its stability on the transport stretcher while carrying the patientload. As illustrated in FIG. 4 d, the arches may be extended around theposterior of the patient to form a continuous or near continuouscylinder. This extension of the arches provides a continuous geometrythat is extremely rigid and appropriate for a cantilevered patientsupport strategy.

In FIGS. 4 a and 4 b, the patient support structure 2 may becantilevered over the interventional volume 76 as indicated. This designmaximizes access to the breast (not shown). In order to preventseparation of the patient support 77 from the stretcher 78, slidingconstraints 79 are incorporated to prevent tipping. Also indicated inFIG. 4 a, is the addition of positional tracking devices 80 into thebody of the stretcher. Removable handles 81 ensures full access tobreasts.

In FIGS. 4 b and 4 b 1, the matched fit of the curved arch 83 into thecurve of the MRI bore 83 is shown.

This cantilevered approach of FIG. 4 provides the maximum real-estateand access in the vicinity of the breast for ancillary instrumentationsuch as US (ultrasound) imaging probes, therapeutic devices andpositioning systems and to maximize access to the breasts from medial,lateral, superior-inferior or oblique directions for breast manipulationor interventional procedures. Also present may be an embedded positionaltracking system. By integrating a positional tracking device into thestretcher (not restricted to, but including optical and magnetictracking devices) at a position that provides line-of-sight, orreasonable proximity to the interventional volume t enables orsignificantly simplifies the procedures discussed further in thisdocument.

FIGS. 4 c 1, c 2 and c 3 show alternative linear guides for the patientsupport guides. In FIG. 4 c 1, a tongue 90 in the stretcher fits into agroove 92 in the patient support to prevent rotational movement. Thisprovides a cantilever bed with the sliding constraints. In order for thecantilevered patient support design not to overturn during patienttransport, it is necessary to constrain the motion of the patientsupport to move in and out of the bore of the magnet (S/I patientorientation). Some possible alternative embodiments of motionconstraints are illustrated as FIG. 4 c 2 and FIG. 4 c 3.

FIG. 4 d shows a modification of the arch structure 91 of thecantilevered design. The arches 91 in this illustration have beenextended to form a complete cylinder around the patient. The openingprovided in the arch structure 91 still enables access to the breast inthe manner illustrated in FIGS. 2 c and 2 d. The degree to which thearches are extended around the patient is dependent on the structuralstrength deemed appropriate. Furthermore, the opening of the arch 91 maybe widened in the Superior/Inferior direction resulting in more accessto the breast at the expense of a relatively weaker structure.

FIGS. 5 a (1 and 2)-c shows only the plate locking system 104 of thepatient support 100 and the related apparatus. The compression plates102 can be moved anterior/posterior within the plate locking support104. The compression plates/locking supports 104 can be introduced fromthe side of the apparatus. FIG. 5 a 1 is a side view and FIG. 5 a 2 is abottom view. Each plate can be moved independently and to any positionin the left/right direction. Additional compression plates in thesuperior/inferior direction can be accommodated so as to “box” thebreast. In FIG. 5 b, are shown height adjustable plates 112 and a guide116 for the anterior-posterior compression plate that slides left andright. Various embodiments of rail positions that are possible are shownin FIG. 5 c, as well as flexible sling 124 designs to compress thebreast against the chest wall. Alternative locations for plate lockingguide rails 120 are also shown.

Compression System

In the method of the present technology described herein, each breast iscompressed in the medial-lateral direction by a pair of compressionplates that are in turn held in place by a pair of plate lockingsupports (FIGS. 5 a 1, 5 a 2, 5 b, 5 c). “Compression plates” may have anumber of different designs as described in the practice of thistechnology. Two or four compression plates may be used at a timedepending whether unilateral or bilateral applications are beingperformed. The plate locking supports may be constrained to move alonglinear guides in a medial/lateral direction. They may be free to beremoved completely or added from the left or right sides of the patientsupport while the patient is lying on it. The height of the compressionplates in the anterior-posterior direction can be adjusted along alinear guide fixed to each plate locking support. The compression plateslikewise can be added or removed from the plate locking supports fromthe top or bottom, though only from the bottom when the patient is abovethem. Both plate locking supports and compression plates arecontinuously adjustable across the entire range of their support, do notinterfere with one another and can be locked in place. The systemillustrated in FIGS. 5 a-c shows two guide rails 120 to support thecompression plate. With two guided rails on one side, this provides acompletely open geometry toward the opposite end of the compressionplate to maintain greatest access. However, with such a geometry, thecompression plate may not demonstrate adequate rigidity that can beovercome by placing one guide rail at the opposite end of thecompression plate. Similarly, using multiple guide rails placed at eachend of the compression would further stiffen the system. In thesefigures we have illustrated the guide rails to be rods and thecompression plates are fitted on the guide rails with linear bearings.Multiple configurations are possible, including the use of T slots anddovetails as dictated by the space available for these mountingstructures. The locking mechanism for the compression plate could beformed by a simple cam mechanism or ratchet and pawl structure whichallow the use of one hand to both secure (lock) and position thecompression plates. The positioning of plate-locking guide rails 120 canbe variously positioned as shown in FIG. 5 c.

Rail systems and tongue-and-groove compression plate support systemshave been presented in the prior art. The design presented by Kuhl,1997, demonstrates a dual rod system. This design differs significantlyfrom the presented embodiments in that the medial and lateral plates cannot be independently positioned, there is only provision for access toone breast at a time, and both plates can not be removed with thepatient on the apparatus. Other designs presented in the prior artincluding U.S. Pat. No. 5,913,863, U.S. Pat. No. 5,855,554, U.S. Pat.No. 6,423,076 do not detail the compression apparatus, or demonstratelimited ability to position the plates as described by Kuhl 1997 (C. K.Kuhl, A. Elevelt, C. C. Leutner, J. Gieseke, E. Pakos, and H. H. Schild,“Interventional breast MR imaging: clinical use of a stereotacticlocalization and biopsy device,” Radiology. vol. 204, pp. 667-675, 1997)and Heywang-Kobrunner 1999. (S. H. Heywang-Kobrunner, A. Heinig, and R.P. Spielmann, “MR-Guided percutaneous excisional and incisional biopsy,”European Radiology, vol. 9, pp. 1656-1665, 1999.)

Another aspect of the present technology enables compression of thebreast in the anterior/posterior direction. This is a particularlybeneficial feature because US imaging and interventional procedures areoptimized by increased breast contact with the compression plates.According to this technology, this can be accomplished by compressingthe breast into a box-like shape as illustrated in FIG. 5 c. U.S. Pat.No. 5,706,812 to Strenk et al. discloses an inflated bladder whichimproves access to the breast during US imaging. However, unlike thepresent technology, the invention disclosed by Strenk et al. does notprovide for equivalent access to the lateral and medial sides of thebreast during imaging and interventional procedures. This concept may befurther extended to include rods, pointers, convex or concave surfaces,or the like that are attached to the compression plates and/or thepatient support structure that perform the function of improving breastcontact with the compression plates.

Another feature of the present technology is the ability to move andlock the medial and lateral plates independently through the platelocking supports using just one hand. This enables the operator tocompress the breast with one hand, while locking it in place with theother. The ability to adjust the positions of the plates along theentire width of the bed is a useful feature which accommodates thevarious sizes of patients and various clinical applications (e.g.medial/lateral interventions, bilateral imaging). Another further aspectof the invention enables movement of the plates in the verticaldirection during compression. This allows the operator to position theplate as close to the chest wall as possible. In the method of theinvention, compression plates inserted into the plate locking supportsmay take different forms as described in the following section of thisspecification. The present technology provides a method to quicklyinterchange plates for various functions by vertically loading theplates into the plate locking supports. Furthermore, compression platesmay be introduced or removed with the patient still on the apparatus byway of removal or addition of the plate locking supports (FIGS. 5 a 1and 5 a 2).

Compression Plates

According to the present technology, numerous functions are accomplishedusing various types of compression plates. These functions include:

-   -   1) MR imaging coils: various coil arrays—single or multiple per        compression plate.    -   2) Interventional plates: multiple hole plates, fenestrated        plate as shown in FIGS. 6 c, 8 (with various aperture shapes)    -   3) US-transparent membrane and membrane support frame which is        -   a. Reusable for imaging        -   b. Can be sterilized        -   c. Can be cut to allow incisions in the breast        -   d. Tension adjustable to adjust flexibility and conformation            The compression plates also holds a breast immobile while a            fenestrated plate in contact with it is moved

The plates disclosed by this invention can be sterilized and can holdseveral fiducial markings 140 (e.g., FIG. 6 a) visible on MRI which actas reference points between the MR images and the physical space. Theplates can also have attachment points for MR imaging coils (FIG. 6 b),needle positioning apparatus (FIGS. 10 a and 10 b) and US transducerpositioning systems (FIG. 6 e). The design and function of these plateswill be discussed in detail in a subsequent section of the specificationin the context of their clinical use. A plurality of compression platesthat may be used according to the technology are identified on FIGS. 6a, 6 b, 6 c. The compression plates may be positioned at any of the 4compression points (left medial, left lateral, right medial, rightlateral) on the breast in any combination required. FIG. 6 c showscompression plates with fenestrated plates 146. FIG. 6 e shows atransducer 148 and a positioning stage 150. These coils can beinterchanged in a modular fashion to maximize and optimize the numberand types of coils used, whether for unilateral or bi-lateral imaging orintervention. Modular coils may also provide either large or small coilsof various designs, RF shields, and coils for different field strengthand field shapes.

FIG. 7 shows various coil configurations a, b, c, d, and e from an axialview of a patient on the apparatus. a) shows a Bilateral imagingapplication with 4 coil array. b) shows a Unilateral imagingconfiguration with 4 coil array. c) shows a Bilateral imaging with 4coil array 160. In order to reduce coupling between the medial coils,their size has been reduced and an RF-shield has been inserted (attachedto sternum support) to limit coil interactions. This shield may take avariety of forms all with the same purpose—passive medial coildecoupling. d) shows RF-shields have been attached to the medialcompression frames. e) shows that Coils may also be attached to the A/P(anterior/posterior) compression plate and used with any of theaforementioned coil geometries. In all cases the maximum number ofallowable coils, for the maximum number of data collection channelsshould be used. A sternum support 162 is also shown, as well as asternum support with RF shield 164, and RF-shields attached to themedial compression plates 166.

Imaging Coils

MR imaging coils are considered in this technology. In one embodiment,the coils may be incorporated into the system by being embedded into thecompression plates as by way of non-limiting examples, using fixtures122 for coil attachment in FIG. 6 a. In another embodiment, the coils138 may be attached to the outside of the interventional or UStransparent plates 142 as shown in FIG. 6 d. In another embodimentadditional coils may be embedded into the patient support structure. Inanother embodiment, the coils may be positioned as close as possible tothe breast in order to produce higher-quality images. The MR coils mayconsist of a single pair of coils per breast (1 medial, 1 lateral), oran array (more than two coils, multiple pairs of coils) per compressionplate. Further enablement for coil configurations per se may be found inSchneider et al., “An Apparatus for MR-Guided Breast Lesion Localizationand Core Biopsy: Design and Preliminary Results,” Journal of MagneticResonance Imaging, vol. 14, pp. 243-253, 2001, which is incorporatedherein by reference. However in that description, no attempt was made tomaximize the number of coils used for imaging unilateral or bilateralanatomy. As a comparison, in the description provided by Greenman, etal., MRM 1998, no attempt was made to ensure the medial and lateralplates could both be positioned as close as possible to the breastthrough an appropriate compression system to maximize image quality. Inthe present technology, moving the medial coils further from one anotherwould provide reduced coil decoupling and limit the issue of coilinteractions and the complexity of coil switching circuitry.Furthermore, no attempt to substitute coil arrays so as to maximize thenumber potentially used for unilateral or bilateral imaging without hasbeen made.

The present technology can also provide for coils specific to differentsized patients. A different set of coils could be used for needlepositioning sequences than those used for simple imaging. These coilsfor needle positioning would have a large central opening through whichneedles could be placed and would be mounted over top of othercompression plates (e.g. a fenestrated plate and/or US transparentmembrane). According to the invention, these coils would be removableand their positions on the underlying compression plate would beadjustable to ensure clearance from a device being inserted into thebreast.

Fiducial Marker System

In the methods of the present technologies, device delivery may be basedon the use of MR-visible fiducial markers as a reference between MRimages and physical space. “MR Imaging-guided Localization and Biopsy ofBreast Lesions: Initial Experience,” Radiology. vol. 193, pp. 97-102,1994, and Kuhl et al., “Interventional breast MR imaging: clinical useof a stereotactic localization and biopsy device,” Radiology. vol. 204,pp. 667-675, 1997 describe the use of fiducial markers placed at a knownposition on the embedded or attached apparatus. The more referencepoints that are used, the more accurate is the registration of the twospaces (physical/imaging). Various embodiments of the fiducial markersmay be used. The fiducial markers may be embedded into some compressionplates in the apparatus for simplicity. In other structures, such asfenestrated plates which may be moved relative to the breast during aprocedure, the markers may be removable. They may also need to beremovable if they may not be sterilized. Device targeting and trajectorycalculations can be automated if the fiducials are at a known positionon the apparatus. Another embodiment of fiducial marker arrangementsincludes a detachable plate which may be positioned at a fixed positionin the compression frame relative to the fenestrated plate positions(e.g. FIG. 18 a).

MR Breast Imaging

The prior art references indicate that the majority of breast imagingprocedures involve simple contrast-enhanced breast imaging withoutintervention. It is important to have a system that is capable of singleor bilateral breast imaging for screening, diagnostic or surgicalplanning purposes.

According to the present technology described herein, both unilateraland bilateral breast imaging procedures can be performed with the simpleremoval and replacement of compression plates containing coils and coilarrays and the removal and replacement of the central support member(used in bilateral imaging) with various support members. The additionof coil decoupling mechanisms such as coil windings, specially designedconductive layers, and electronically active blocking circuits into thespace between the two coil pairs is enabled by the open architecture ofthe apparatus of the present technology. One embodiment includesattachment of the mechanism (illustrated in FIG. 7 as an RF shield), tothe bottom of the central support member. Quick attachment of thismember enables easy preparation of the system for various imagingpurposes. Alternatively, more than one RF shield could be introduced andmounted on the guide rails to be positioned in a patient-specific mannerto optimize imaging performance. The open architecture disclosed in thisinvention further enables improved access to the breast for the operatorfor breast positioning before imaging. The addition of lighting and amirror system enables visualization of the breast. The ability to seethe nipple and the ability to move the medial and lateral platesindependently facilitates having the nipple pointed downward and in themiddle of the imaging field. This is important as the nipple is used asa reference point for the radiologist. Furthermore, the ability to movethe plates up towards the chest wall ensures optimal compression of thebreast ensuring there is minimal motion during the procedure.

According to this invention, the ability to use different coilconfigurations for different purposes (bilateral, unilateral) and toaccommodate various patient breast sizes (e.g. one set for large, oneset for small breasts) is critical to acquire optimal images. Dependingon the number of data acquisition channels in the MR imaging system,multiple coil arrays can be used. Various coil geometries which may beused in the method of the invention are presented in FIG. 7. Thisconcept of removable coils has not been presented in the prior art withrespect to 1) providing the maximum number of coils for the imagingapplication (bi-lateral, unilateral, interventional imaging) so as tomaximize the number of active data collection channels. 2) Adjustingcoil arrays for smaller or larger breasts, 3) Upgrading coils and coilcabling as the associated MRI system is upgraded for increased number ofdata channels, 4) Providing coils operating at different frequencies forhigher magnetic field applications. The ability to easily remove coilsand exchange them for other coils without modification of the mainimaging structure is a critical feature enabling optimized imaging andinterventional functions with a single apparatus.

MR-Guided Breast Interventions

Various breast interventional procedures are enabled by the apparatusand method of the present invention. The ability to perform core biopsy,wire localization, lesion marker placement, guide tissue ablationdevices and placement of tissue therapy devices (chemotherapy,radiotherapy, cryotherapy, heat therapy, gene therapy) are some of theclinical applications enabled by the invention. Apparatus and techniquescommon to these procedures are presented in the following section.

MR-Guided Device Delivery

The ability to accurately deliver a plurality of needles to a lesion orto multiple sites within the breast using MRI guidance is a fundamentalaspect of the present invention. According to the method of theinvention, fiducial markers can be used as reference points, so that theoperator can position various MRI-compatible needles (e.g. titanium andcomposite needles) ranging from fine aspiration needles (approx 24 gauge(0.51 mm)), to wire delivery needles (20 gauge, (0.81 mm)), toconventional core biopsy needles (16 to 14 gauge (1.29 mm-1.63 mm)),coaxial introducer needles (14 to 11 gauge (1.63 mm-2.30 mm) toaccommodate the core biopsy needles), and large vacuum assisted biopsyneedles and their introducer needles (14 to 9 gauge (1.63 mm-2.91 mm),or larger). The ability to infer needle position using signal voidproduced by needle susceptibility artifacts is well established in theprior art, for example, U.S. Pat. Nos. 4,989,608 and 5,154,179 toRatner, U.S. Pat. Nos. 5,744,958 and 5,782,764 to Werne, and U.S. Pat.No. 5,944,023 to Johnson et al.

Delivery of hollow needles for purposes such as acquiring tissue samplesby biopsy, or implanting wires or other markers as guides for surgicalexcision is founded on the same general procedure. Initially the breastof interest is compressed between two plates designed to allow needleaccess to the breast. These plates may take many different forms asindicated in FIG. 8. One embodiment consists of a plate with a largenumber of apertures to guide needles of interest. Other plates contain aseries of apertures of specific shapes and size which provide access tothe breast to prepare for intervention by injecting local anesthesia andmaking a skin incision. These are known as fenestrated plates. An arrayof square apertures have been disclosed in prior art references, forexample, U.S. Pat. No. 5,855,554 to Schneider et al and U.S. Pat. No.6,423,076 to Cardwell et al. Various other implementations may includecircular, triangular, hexagonal, or other aperture shapes, with variouspositioning, or packing orientations on the compression plate 180 asindicated in FIG. 8. Each plate 180 may have features 181 for positionaladjustment (e.g., anterior-posterior). Each fenestration preferably hasan asymmetrical shape to assure proper orientation within the supportassembly 182 that has a membrane 142, fixture for fenestrated plateattachment 183, and fixture for orienting coil attachment 185. There maybe keyed fenestrations 186 and ultrasound transparent membranes 187 inthe assemblies of the compression plates 180. Needle guidance isaccomplished by installing a guide plug with appropriate cross sectionin one of the apertures. These guide plugs have bore-holes sized toguide interventional devices (such as needles) of various gauge sizesand lengths. The simplest implementation involves an array of holes in aplug sized to fit into one of the fenestrated plate's array ofapertures. These smaller holes act to guide the needle into the breastin a straight manner, minimizing the tendency for the needle to deviatefrom a medial-lateral trajectory. Other types of needle guide plugs canbe used with the system. For a particular fenestrated plate, a number ofguide plugs can be provided to accommodate various needle gauge sizes.

The procedure of MRI needle guidance according to the invention isdemonstrated in FIGS. 9 a, b and c. A typical example of such a fixationframe 200 is shown in FIG. 9 a, which serves to hold the breast 220 in afixed geometry during the biopsy procedure and also support MRI-visiblefiducial markers 204, which are used for subsequent registration. Theframe 200 holds the breast while the patient is in a prone position inthe MR system. The frame holds the breast in a medial-lateral direction.The biopsy needle 202 and MR coils 203 are shown. A cancer lump 212 isshown within the breast 220 and guide holes 208 are shown in the guideplate 206. Plug inserts 214 are shown for the window assembly 216. Otherorientations such as cranial-caudal or oblique are possible, howeverhave not been presented in the prior art to our knowledge. A means ofMRI-guided needle delivery as indicated in FIG. 9 has been presented invarious forms in the Prior Art (Orel et al., Radiology. vol. 193, pp.97-102, 1994; Kuhl et al., Radiology. vol. 204, pp. 667-675, 1997;Fischer et al., Radiology, vol. 192, pp. 272-272, 1994; Doler et al.,Radiology, vol. 200, pp.863-864, 1996; Fischer et al., Radiology, vol.195, pp. 533-538, 1995; Heywang-Kobrunner et al., European Radiology,vol. 9, pp. 1656-1665, 1999; Liney et al, Journal of Magnetic ResonanceImaging, 2000, Su (U.S. Pat. No. 6,163,717), Fischer (U.S. Pat. No.5,913,863), Cardwell (U.S. Pat. No. 6,423,076)) and embodied incommercial breast imaging devices by MRI Devices Inc, USA Instruments,MachTech Inc. The basic premise of this approach is not novel for use asan MRI-guided needle positioning method. This prior art forms the basisof many of the inventions described further in this document whereguidance of needles based on fiducial markers at known relativepositions to fenestrated guides and plates is required. Differingfeatures are highlighted where appropriate with respect to MRI-guidedneedle insertion and the associated apparatus.

Fundamental to MR-guided needle guidance in the manner described aboveis a compression frame constructed of a fenestrated plate 206, whichserves to accept a guide plug 214. As shown in FIG. 9, this holder hasan array of small apertures, on close centers. Fiducial markers 204 areplaced on the grid array of the window assembly 216 and imaged alongwith the breast 220 during the MRI aspect of a procedure. These markers204 are visible in the MRI data set along with the suspicious mass 212.By measuring the location of this mass relative to the fiducial markersin the image, the exact location of the lesion can be determinedrelative to the grid array frame in physical space.

According to the invention, it may be desirable to deliver devices tomultiple locations within the breast (e.g. core biopsy requiringmultiple core samples) or to bring the device along an obliquetrajectory. In these applications, limiting the needle orientation to astraight (medial to lateral) trajectory is undesirable. Positioning theneedle in a straight manner limits the accuracy, which the needle may bepositioned, and multiple samples would require multiple skin incisions.Since device delivery can only be achieved through a finite number ofholes, the specificity of device positioning is limited. So for someapplications a different guide plug capable of defining an angled needletrajectory is required. An embodiment of such a guide plug 230 is shownin FIG. 10. It is composed of a gimbal 240 which allows rotationalfreedom in two directions. The needle guide 232 is a hollow tube passingthrough the centre of the gimbal 240 which allows free rotation of thegimbal 240 about a centre of rotation in the insert form 238. By turningthe clamp 234, it is possible to lock the needle guide orientation. Welater propose a goniometer to set this orientation (FIGS. 11, 12). Sucha design for a gimballed guide plug has been demonstrated in previousU.S patent documents (U.S. Pat. No. 6,195,577 Truwit et al, U.S. Pat.No. 6,267,769 Truwit, and U.S. Pat. No. 6,368,329 Truwit) and isembodied in the Navigus brain biopsy system developed by Image GuidedNeurologics, Inc. However, the design of the system of the presentinvention is substantially different in that the base of the guide plugcan only be positioned in the slots of the fenestrated plate in oneorientation. Furthermore, the present invention can be furtherdistinguished from the prior art because the plug is constructed so asto minimize the variations in the needle entry point for varying anglesof the gimbal as discussed above This is desired to provide a commonentry point to the skin for gathering multiple tissue samples. As such,it is desired to have the design optimized such that the centre ofrotation of the needle 233 is close to the surface of the skin in orderto facilitate multiple needle entries at different needle trajectorieswithout the need to increase the size of the incision as discussedabove. This can be achieved by removing a portion of the gimbal is shownin FIG. 10 to create a flat zone which is applied to the skin surfacewhile still providing a spherical surface for rotation and locking ofthe gimbal. In FIG. 10 b, the insert form 250 is shown with analternatively designed gimbal 252.

Once the gimbal is set, its orientation relative to the fenestratedplate must be fixed. This is accomplished by the use of a key or someother unique shape which aligns with a feature in the fenestrations ofthe compression plate. Based on the MRI coordinates, the lesion 260location is defined by two angles shown as α and β, and an insertiondepth z as shown in FIG. 11. The angle β determines the offset angle ofthe needle trajectory 262 from a perpendicular delivery into the tissueand describes a cone with its apex at the center of the needle gimbal264. The surface of the cone passes through the lesion at azimuthalangle α on this cone surface. To prescribe these two angles to the guideplug, a goniometer 270 may be used as shown in FIG. 12. This device is asimple mechanical structure, provides specified orientation of theneedle (not shown) in the gimballed guide plug 272 prior to insertion.The guide plug 272 is placed in the keyed guide plug disc or needleholder disk 274 and a sterile needle guide extender 276 is placed overthe needle guide plug disk 274. This extender is used to deliver thedesired angles in the goniometer system. First the guide plug disc 274is rotated to angle α and the guide plug slider clamp 278 is secured topreserve this angle on the slider ring 280. Then the slider clamp isrotated to define the angle β as shown, after which this is also clampedto prevent further motion. To preserve the orientation of the guideplug, a clamp on the guide plug 234 is activated to lock the gimbal andneedle holder in position. The guide plug can be removed and insertedinto the fenestrated array. Once in position, the needle is advanced thenecessary distance as determined from the MRI data to intersect thelesion as desired.

In order to ensure sterility throughout the procedure, the guide plugdisc, guide plug and needle guide extender can be sterilized for eachpatient, or may be disposable items. If multiple biopsies or entriesinto the tissue are needed, multiple guide plugs can be used, each ofwhich are positioned to the desired location by the goniometer prior toor during the biopsy procedure. With each guide plug pre-set, or setelsewhere by an assistant, the biopsy procedure can be efficient andrapid.

According to the present invention, it is possible to introduce a deviceat an arbitrary orientation while preparing another device orientationin a separate guide plug using a goniometer. The design and use of agoniometer to define and set the position of a guide plug forinterventional procedures is unique with respect to the prior art.Attempts to precisely define angulations through mechanical apparatus atthe site of interest have resulted in bulky and inappropriate devices asdemonstrated in U.S. Pat. No. 6,048,321 by McPherson et al, and aneurological application U.S. Pat. No. 5,984,930, by Maciunas. Specificimplementations for breast biopsy include U.S. Pat. No. 6,423,076,Cardwell et al, and Heywang-Kobrunner 1999. These designs differ in thatthe angular position of the needle is defined by an apparatus attachedto the compression frame immobilizing the breast. In this manner, largebulky apparatus are required and limited angulation is available.

Various embodiments of the fenestrated plates, gimballed plug andgoniometer are possible according to the invention. The apertures of thefenestrated plates, the base of the guide plug and the correspondingaperture in the goniometer are of the same cross-section (e.g.,circular, square, triangular, hexagonal, etc). Furthermore thegoniometer would serve the same purpose if either the arch or the disc(but not both) subtended only one-half of the range shown (i.e. either90 degrees or 180 degrees respectively).

In the method of the invention, the needle can be introduced from eitherthe medial or lateral sides of the breast by placing a grid plate on thecorresponding side of the breast. The needle trajectory ispreferentially determined such that the minimal amount of breast tissueis traversed, however in cases where many needle passes may be required,a constraint to minimize the number of skin incisions and make allpasses through one aperture may take precedence. This system enables aflexibility to allow for many different needle trajectories to approachthe lesion. Similarly, it allows the needle to be introduced atarbitrary angles to ensure safe and appropriate insertion of a needleinto a tumour. For example, for lesions near the chest wall, it isimperative that the needle follows a path parallel to the chest wall andnot inclined to it, so that the possibility of chest wall penetration iseliminated.

A weakness with a fixed fenestrated plate is that various regions ofbreast tissue are inaccessible to the needle (areas at the edges of thefenestrated plate and those occluded by the material of the plateitself). Due to limitations on the angulation of the gimballed guideplug, large areas of tissue may be inaccessible. A solution to this isprovided by the present invention as shown in FIG. 13. By decoupling thetwo functions of compression/immobilization of the breast andstereotactic frame, accessibility of the breast tissue can be optimizedto minimize the effects of “blind-spots” in the breast. This fenestratedcompression plate consists of a frame 292 with a sterile plasticmembrane 294 pulled taut across its surface that can be cut andpunctured with a scalpel or a needle (e.g., Opsite™ surgical material,or other membrane transparent to ultrasound). This plate is used tocompress and immobilize the breast. Attached to this frame/membranecombination on the side opposite the breast is a fenestrated plate 290as identified in FIG. 13. This effectively decouples the function of theprevious embodiment of the stereotactic frame: the film compresses thebreast, while the frame provides a plug and needle guidance referenceframe). Fiducial markers 296 may either be attached to the compressionplate 292 or the fenestrated plate 290. The fenestrated plate 290 mustbe designed such that it can be attached to the frame in variousorientations, adjustable for position such that the fenestrations can becentered over different regions of breast tissue. Removing thefenestrated plate and repositioning it into the frame at a differentorientation, or adjusting its position (in superior-inferior oranterior-posterior directions) without removing it would provide accessto tissue which would otherwise be occluded. When the fenestrated plateis moved or removed, the breast would not move relative to thecompression plate, as the function of breast compression andimmobilization is provided by its membrane. Different embodiments ofthis concept are illustrated in FIG. 13. Furthermore, it is important todistinguish that required repositioning of the fenestrated plate toaccess previously inaccessible regions depends on whether fenestrationsare organized in a hexagonally package structure or a rectangular gridand indicated in FIG. 14. For example, in this figure, consider adesired point for biopsy 300. In the various fenestrated plateorientations, the openings have been shifted (by shifting thefenestrated plate within the frame) to assure that the desired targetpoint 300 is accessible through a hole 302. The plates may be shiftedup, down, left and right to align the hole 302 with the target point300. If we had a rectangular grid of holes moving the plate up does notput the point at the centre of a hole. A second repositioning of theplate is required in the S/I direction. As such hexagonal arrangementsare more efficient. As mentioned previously, many fenestrated platesystems are available, and have been presented in the Prior Art. Howevernone have demonstrated the ability to decouple the function ofcompression and providing a stereotactic frame. This invention providesa significant advantage to access the “blind-spots” associated withfenestrated plate stereotactic systems.

According to the invention, both straight and angled needle trajectoriescan be determined with a calculation based on various criteria:

-   -   Adopt shortest needle path to target (medial or lateral approach        as appropriate, minimal angulation of needle).    -   Limit multiple samples through a single fenestration.    -   Select arbitrary fenestration—determine appropriate needle        trajectory.    -   Avoid patient support apparatus and other equipment.    -   Avoid anatomical features such as chest wall.        Needle Position Verification:

According to the invention, for all MR-guided needle guidancestrategies, MRI verification is required to ensure the needle ispositioned appropriately. However a strategy that includes softwareverification of the needle trajectory before needle insertion can beembodied in the needle trajectory guidance software. Visualization ofthe planned needle trajectory on the MR image set used to identify thelesion can be accomplished by superimposing an indicator on the MRimages. This is particularly important to identify the expected positionof biopsy needles after insertion.

Identification of the lesion after needle insertion may be difficult insituations where the lesion is smaller than the artifact generated inthe MR image. According to the invention, software may be implemented todetermine whether the lesion has moved after needle positioning. Imagingalong the length of the needle (axial image acquisition corresponding toa needle trajectory in the medial/lateral direction), enablesvisualization of the needle depth. Identification of anatomical featuresof the breast before and after needle insertion provides a comparison toidentify whether there has been gross motion of the lesion (inferringlesion motion from the surrounding interfaces when the lesion cannot beidentified). MR images acquired before or after contrast agent injectionprior to needle insertion can be compared to images acquired afterneedle insertion. Scaling and registration of these images, detection oftissue interfaces in the images and determination of the differences inthese edge positions enables measurement of the tissue motion afterneedle insertion. In cases where there is large tissue deflection and/ordeformation, the needle position may be corrected.

EXAMPLES OF CLINICAL APPLICATIONS OF THE INVENTION Example 1 MR-GuidedWire Localization

The use of device guidance techniques to deliver a localization wire ormarker to guide surgical intervention is illustrated in the flowchartshown in FIG. 25. The patient is first positioned on the patient supportapparatus. The breast of interest is then compressed between twofenestrated compression plates with attached fiducial markers, which areattached in turn to the compression plate locking supports. Thesefenestrated plates are sterile and can be introduced while the patientis in the prone position. These plates can be moved in theanterior-posterior direction to positions near the chest wall to enablefull interventional access to the breast. MR imaging coils are attachedto these compression plates. MR imaging is then used to identify thelesion and the fiducial markers. Using this information, the appropriatefenestrated plate aperture and needle guide plug hole are determined inorder to position the needle as closely as possible to the desiredtarget position. Medial or lateral needle trajectories will be selectedto minimize the depth of tissue being traversed, depending on theposition of the target within the breast.

The patient is then removed from the imaging magnet and the marker guideneedle (which is hollow in order to permit delivery of markers throughit) is inserted according to the trajectory calculations. If more accessroom is required, the interventional volume below the breast may beaccessed by retracting the bridge in the transport stretcher. The MRIcoils may be removed as required to provide more access to the breast,and can be repositioned on the compression plates in order to reduce anyinterference with the marker guide needle or wire/marker. The transportstretcher's bridge is replaced. Walls on the side of the stretcher'sbridge may be used to ensure clearance of all devices from the magnetbore. The patient and patient support are next advanced back into themagnet bore and MRI is used to validate the needle position. Strategiesto determine if surrounding tissue has deflected in cases where thelesion may not be well visualized may be implemented based on the imagesacquired. The needle position may be repositioned and again verified forposition. The final step entails insertion of the wire or marker intothe tissue through the hollow guide needle and removal of the needleleaving the wire or marker in place in the breast. The guide plug,fenestrated plate and compression plates may then be removed from thebreast and the interventional procedure completed.

Example 2 MR-Guided Angulated Breast Biopsy

According to the invention, a core biopsy needle may be delivered to thebreast on an oblique trajectory as illustrated in the flowchart shown inFIG. 26. A needle guide plug having straight (medial-lateral) holes of alarger diameter than the biopsy needle, or angulating guide plugs may beused in cases. Patient positioning with fenestrated plates and MRimaging is performed in an identical manner as described under MR-guidedwire localization, with the option of implementing the variouscompression plates indicated in the diagram. Calculation of the needletrajectory is done using compound angles to define the needle trajectoryand a goniometer is used to set the orientation of the guide plug. Incases where access to some targets is limited by the fenestrationaccess, the fenestrated plate's position may be altered without movingthe breast.

Introducer needle insertion is preceded by producing an incision in theskin at the center of the fenestration to facilitate needle entry intothe breast. MR validation of needle position is performed before thebiopsy sample is taken. In cases where small corrections in needleorientation are required, the guide plug gimbal can be unlocked and theneedle orientation corrected by hand. In cases where a large correctionis required, a new needle trajectory can be calculated based on the MRIvalidation images and a new guide plug orientation defined. In caseswhere multiple samples are required, multiple guide plug orientationsmay be defined in parallel with biopsy sample acquisition. Varioussystems in clinical use (Koebrunner 1999, Kuhl 1997) use angulatedneedle trajectories to acquire multiple samples, however this techniqueis unique in that the definition of the guide plug orientation is doneaway from the patient with the use of a goniometer. This enablesmultiple trajectories to be prescribed rapidly and accurately (currentlyin with an included angle of 60 degrees).

Example 3 MR-Guided Marker Placement

The concept of MR-guided biopsy presented in Example 2 can easily beextended to placement of small position markers in the breast, accordingto the invention. This may or may not be done in conjunction withMR-guided biopsy, or done in conjunction with MR-guided needlelocalization. This application would take advantage of the fact that alarge tissue segment can be accessed through a single incision point(repositioning of the fenestrated plate to provide better access may berequired). As shown in FIG. 15, a linear tumor 320 can be delineated byway of a set of markers 326 These markers 326 may be identified afterthe procedure defining the maximal extent of the tumor. Markers such asendovascualar occlusion coils, surgical clips, or any of the devices asdisclosed by Foester et al. in U.S. patent application Ser. No.2002/0193815 A1 may be used. Furthermore, radiotherapy implantableseeds, or local chemotherapy delivery devices may also be distributedaround the periphery of the tumor. Clips can be delivered through thecenter of a hollow needle 324, and when fully extended and uncoiled,they remain fixed in the tissue at the end of the needle 324. Theseclips would have to be made of the appropriate MR-compatible material(e.g., titanium, platinum, stainless steel, etc.) to ensure they can beidentified and do not compromise subsequent MR images, and to ensurethey can be safely used within the MR magnet room. The use of thisprocedure according to the invention is illustrated in the flow chartshown in FIG. 27.

Example 4 MR-Guided Interstitial Therapy Delivery and Monitoring

In the method of the present invention, the techniques described abovemay be easily extended to deliver a variety of tissue investigation orablation devices such as invasive ultrasound tissue ablation devices,RF-heating devices, cryotherapy systems, local delivery ofchemotherapeutic agents, local delivery of radioactive material fortherapy, optical ablation (lasers), optical photodynamic systems or anyother tissue destruction technique. Monitoring of these devices may bedone using MR imaging to measure temperature distributions, chemicalconcentrations or other parameters during therapy. In the case of theoptical systems, the treatment region may be defined using othertechniques (i.e. T2-weighted contrast sequences).

MR/US Hybrid Imaging and Intervention

With the system outlined above, an apparatus for delivering a device toa lesion is described with an arbitrary trajectory. However, the needlepath may deviate from the planned trajectory due to either tissueheterogeneity which can cause needle deflection. A hard lesion andsurrounding tissue may move during device entry. Further, the ability tobiopsy small lesions can be limited due to the size needle-generatedartifact on the MR images as previously mentioned. This is particularlyproblematic when preformed on a high field imaging system (i.e., greaterthan 1.5 T magnetic field strength). Ideally, a means to observe theneedle path in real-time is optimal to ensure correct lesionpenetration. According to the present invention, an ultrasound imagingcapability can be added in the same biopsy apparatus in order to delivera US transducer using the same stereotactic delivery strategy asoutlined in the previous section. A device can then be delivered intothe breast under the guidance of this real-time US imaging in severalways.

Through a simple modification to the biopsy system, removal of thecompression plates and substitution with an acoustically transparentwindow held in a frame containing fiducial reference points, theinvention can be used to perform hybrid (MR/US) imaging. This aspect ofthe invention involves detecting the lesion using MRI, than removing thepatient from the MR magnet's intense field to perform US imaging. Usingthe system in this manner constitutes an automated strategy to identifyMR-detected lesions in US images as well as a means of fusing MR and USimages. The real-time US data can be used to position a deviceaccurately into the lesion and to verify its position. This may be doneusing US exclusively when the lesion can be identified on the US image,or using a combination of the MRI and US data if the lesion is noteasily identified using US, or if the patient may have moved.

The approach to breast imaging disclosed by the present invention hasmany useful clinical applications as generally demonstrated in thefollowing examples. These applications can also be extended to existingMR and US imaging modalities (e.g. contrast-enhanced MRI/US, compound USimaging, US Doppler imaging, etc), or to those available in the future,without departing from the scope of the invention.

Example 5 Hybrid MR/US Imaging

This application involves accurate location and assessment of extent ofan MRI-detected lesion using US in the same procedure while the patientremains in the same apparatus that was used for MR imaging. This offersan alternative to retrospective US detection of MRI-detected lesions intwo different procedures. This retrospective technique can be inaccurateand time consuming as the patient is in two very differentconfigurations for both imaging procedures. This relies on the skill ofthe radiologist to mentally transform data from the two modalities.Hybrid MR/US imaging enables the radiologist to confidently identifyMR-detected lesions using US which may allow them to improve diagnosticability based on features visible under US. It also allows them toidentify anatomical landmarks which can be used for subsequent US-guidedbiopsy with the patient removed from the biopsy apparatus. Knowledge ofthe US characteristics of the lesion could lead to easy identificationof the lesion in a follow-up US examination. In cases where the lesionis difficult to identify on the US image, the option to view the lesionas an image where MR and US-visible features are combined.

Example 6 Hybrid Biopsy

This application of hybrid imaging involves biopsy acquisition underUS-guidance while the patient remains on the biopsy table with theirbreast immobilized. The region of interest for US examination isidentified using previously acquired MR images. This procedure involvesstereotactic delivery of the US transducer in conjunction withfree-hand, or stereotactic delivery of the biopsy needle. This may beaugmented by the use of combined MR/US data set, and with or without theuse of a US transducer whose position and orientation are measured inreal-time, and/or tracked biopsy needle. This image can be superimposedonto the MR/US fused dataset in such a way that the needle is easilyidentified on the MR/US fused image set, and in a way that the presentedMR/US image(s) updates with the changing position of the US transducer.

Example 7 Hybrid-Guided Marker Placement

In a similar manner as hybrid-guided biopsy, and in the same way asMR-guided marker placement differed from MR-guided biopsy, this systemcan be utilized to place numerous implantable devices to denote breasttumor extent. In this case the applicator needle placement will beperformed using US-guidance and may be done either using free-handapplicator guidance or stereotactic needle delivery with the ability tocorrect for applicator and tissue deflection. In this case the fusedMRI/US data may provide better determination of lesion boundaries thanUS guidance would give alone.

Example 8 Interstitial Therapy Device Delivery and Monitoring

The hybrid device delivery technique may also be used to deliver devicesother than biopsy needles, or marker placement devices. This system canalso be used to position a variety of tissue investigation or ablationdevices, such as invasive ultrasound tissue ablation devices, RF-heatingdevices, cryoablative systems and, optical photodynamic systems asdescribed previously. In many cases it is advantageous to monitor thetherapy using the US images, particularly using cryotherapy. Thistechnique may offer the ability to improve the accuracy of the delivery,was well as reducing the amount of MR imaging required. Again this canbe done using the combined MR/US data set, or using only the US data ifthe lesion can be confidently identified on the US image. However, theuse of the combined MR/US data may be beneficial as MRI may provide muchbetter definition of tumor boundaries.

In all applications described above, US imaging modes (e.g. Doppler, 3Dimaging, US contrast agents) may improve lesion detection. According tothe invention, various means of image fusion can be used to assist inimage correction in both the MR and US images.

For all MR/US hybrid imaging procedures set forth in Examples 5-8,standard apparatus may be used as outlined in the following section. Themethods are useful for accurate location of the US transducer to allregions of breast tissue, transformation of coordinates between the MRand US imaging data, MR/US image fusion/integration techniques, MR/USimage correction and reformatting. According to the invention, thisequipment can be integrated with the biopsy system presented in theprevious sections, (i.e. the patient support, biopsy table, compressionsystem, MR imaging coils).

US Transducer Delivery

Another aspect of the invention provides the ability to deliver an USimaging transducer to a particular MR-detected position in space usingMR-detectable fiducial references. A US transducer holder andpositioning apparatus is affixed at a known position relative to thesemarkers. If the position of a target on an MR image is known relative tothese MR detected markers, then the position of a US transducer relativeto these same markers can be calculated such that the device and thecorresponding US imaging plane can intercept that target. If the USimaging plane and field of view is known relative to the US transducer,then a transformation from MR to US image coordinates can be obtained.The devices involved include a constraint plate incorporating anacoustically permeable membrane to immobilize the breast, a stereotacticframe with embedded/attached fiducial markings 340 and attachment points344 for a transducer positioning/tracking system 342. FIG. 16, FIG. 17,FIG. 18, and FIG. 18a show these components. FIG. 16 is the positioningstage where a mechanical stage with five degrees of freedom and capableof two different transducer orientations allows accurate transducerpositioning. FIG. 17 is the tracking system with a free-hand positiontracking device 350 and registration apparatus for free-hand tracking352. FIG. 18 shows how a nest 360 may be positioned in two or moreorientations. FIG. 18 a shows touch points 370 at known positionsrelative to MRI visible fiducial markers to provide an alternative meansof free-hand registration.

In the method of the invention, the function of the membrane is toprovide a means to compress the breast as well as provide a window forUS imaging. A polymeric membrane that is acoustically matched and isthin enough to not attenuate the US beam in a manner that affects USimage quality is suitable (e.g., polyethylene, polystyrene, polyester,polycarbonate, etc.). It is important that the breast is well compressedand that the breast is coupled to the membrane (US coupling gel isapplied between the breast and the membrane before the procedurebegins). Designing the membrane such that it bends a small amount toconform to the curvature of the breast ensures that there is maximumcoupling between the breast and the membrane. This allows maximumimaging access to the breast (FIGS. 19 a, b, c, d). Strategies toconstrain the breast in other directions enable full access to all ofthe breast, including regions behind the nipple. In an initialpresentation of this concept devoid of technical details, theanticipated implementation involved US imaging and interventionoccurring on opposite sides of the breast (Plewes et al, 2001 IEEEUltrasonics Symposium). This was the only presentation of this conceptas Prior Art. However this simplistic embodiment without redesignedpatient support for probe and needle angulation capacity and without acompression membrane and breast constraints in other orientations provedto be ineffective for clinical usage. The compression membraneconfiguration presented in FIG. 19 is key to providing complete accessto the breast, and at first glance is not obvious. FIGS. 19 a, 19 c showthat lesion 402 is difficult to access with ultrasound (US) imaging witha taut frame holding the membrane 400 stiff. FIG. 19 b and FIG. 19 dshows compression with a larger, deformable membrane 404 that placesmore membrane in contact with the breast. In FIG. 19 a and FIG. 19 c,the two rigid frames 406 also make the breast difficult to access for USimaging, while in FIG. 19 b, 19 d the curvature 408 (as seen from belowthe breast) allowed with a less rigid or taut system allows the lesions410 more accessibility in US imaging.

According to the invention, the US transducer holding and positioningsystem can take two general forms; 1) a mechanical stage, 2) a free-handtracking device. Both techniques involve holding an US transducer in aconformal nest which is then attached to either a mechanical stage, orto a tracking device at a known position and orientation. A mechanicalpositioning system enables accurate positioning of the transducer withvarious degrees of freedom. This positioning system is then attached tothe compression plate at a known position with the axes of USH motioncorresponding to the MR imaging axes (L/R, A/P, S/I), and therefore tothe physical frame of reference. This facilitates transformationsbetween the MR frame of reference and the transducer frame of referenceas well as eliminating the need to register the positioning apparatus tothe stereotactic frame during the procedure. In the embodiment shown inFIG. 18 the transducer can be moved through 5 or more degrees offreedom. This design, with positioning tracks on the periphery of thebreast imaging volume, enables access to areas near the chest wall,which is critical for complete access to the breast. The rotational axesof the positioning system further enable the transducer to be angled toimage regions of breast tissue that would be inaccessible with a simplehorizontal or vertical imaging approach. The design of this stage allowsfor large angulations of the transducer without interference. Thisdevice ensures that the transducer can be moved in the vertical (A/P)and horizontal directions (S/I) with the transducer face always incontact with the membrane surface. This allows for effective scanningthrough the breast volume, facilitating 3D US imaging applications andalso enables a lesion to be inspected using multiple transducerorientations. This design further enables accommodation of varioustransducers during the procedure by interchanging the transducer nest.The position of the US imaging plane is known because the position ofthe transducer relative to the USH is known. The ability to easilyremove US transducers from the USH allows the radiologist position theUS transducer by hand. Once a lesion is identified in the US image, theUS transducer can be removed from the nest and be manipulated free-hand.This allows visualization of the lesion through multiple imaging planeswhich is known to be a critical element of US imaging, however onceremoved from the nest, the position of the transducer is no longerknown. There are no inventions presented in the Prior Art that pertainto a mechanical positioning stage for an US transducer accounting forthe presented constraints.

The invention also provides another tracking option that more closelyresembles the traditional manner of imaging with the US transducer;namely, a 6 degree of freedom tracking device (or other lower orderdegree of freedom systems) such as an optical (fiber optic),electromagnetic tracking, ultrasonic tracking, or other non-contactposition tracking system in which the transducer is free to move inspace without fixtures. This aspect of the invention accommodates atechnique which is more familiar to the radiologist; however, theaccuracy with which the transducer can be free-hand positioned to aparticular position may be limited. To use such a non-contact trackingsystem to determine transducer position relative to the fiducialmarkers, the orientation of the tracking system must be calibrated tothe orientation of the stereotactic frame, and thereby to the MR imagecoordinates. This can be accomplished by positioning thetransducer/receiver at points on the stereotactic frame at knownpositions relative to the fiducial markers, measuring these positionsand determining a correlation to convert the tracking system coordinatesto the corresponding MR coordinates and vice versa.

In another embodiment of the invention, an algorithm is applied whichtranslates a given MR-detected coordinate to a corresponding USHposition for a given US transducer in a given orientation (vertical orhorizontal for the USH system presented in FIGS. 16, 17, 18 and 18 a),such that the target of interest will appear in the center of thetransducer imaging field at a calculated depth. A US imaging plane canbe identified such that the shortest imaging distance to the lesion isselected, or to intersect the lesion using a specific transducerorientation. This algorithm enables conversion of a single MR-detectedposition to a set of USH axis-positions and a unique position on the USimage. Techniques to register and fuse MR and US images (i.e. more thanone corresponding point at one time) are explained in the followingsection.

Image Integration

The present invention provides a method for registering MRI and USbreast images (2D and 3D images) to various levels of sophisticationbased on accurate stereotactic transducer positioning and/or subsequenttransducer position tracking. By knowing the orientation of the UStransducer, a 3D MR data set can be reformatted to generate an MR imagethat corresponds to what is visualized on the US image (i.e. generate a2D image from the 3D MR image set that is the same scale and size andcorresponds to the same plane as the acquired US image). The actualtransducer position can be determined by either the mechanical systems,or the non-contact transducer position measurement systems presentedpreviously. Presenting the two images side-by-side allows theradiologist to validate that the lesion and surrounding structures inthe US image correspond with the MRI data. Segmentation (imageprocessing) and integration of the MRI data in ways to depict anatomicallandmarks and functional information such as contrast agent uptakeparameters would facilitate identification of the lesion and surroundinglandmarks in the breast. This system can further be enhanced bynon-contact position tracking of devices such as biopsy needles, ortissue ablation devices. Tracking the position of devices permitsindication of the device position on this reformatted MR data andpermits free-hand device delivery without guidance plugs or fenestratedplates. In addition, the real-time position-tracked US image of a devicecan be superimposed onto this image.

There are many tracking systems in the Prior Art related to the trackingof devices for the purpose of display and manipulation of medicalimages. In Comeau et al, (Med Phys, 27(4), 2000) a presentation of suchan integrated system for the purpose of tracking an US probe relative toa patient's skull for the purpose of co-registration with respect to aset of pre-acquired MR images was presented. Here a method of opticallytracking the US probe, and using US information to help correct fortissue shift errors associated with MR brain surgery was presented. Theuse of such a system to assist brain surgery is facilitated by theconstraining nature of the boney skull. Such a concept has not beentranslated to deformable structures such as the breast as there has beenno way to appropriately constrain the breast while providing adequateaccess required for intervention. Furthermore, the proceduraldifficulties associated with previous attempts have precluded itsfurther development. An integrated system as presented in the inventionenables application of image co-registration techniques in a way that isclinically practical.

Similarly, according to the invention, MR data can be displayed with asuperimposed marker indicating the position of the scan plane of the UStransducer. Visualization strategies such as maximum intensityprojection could be used to effectively depict the 3-D MR data in a waythe radiologist can clearly interpret. Furthermore, four-dimensional, ortime series data could be combined and presented as a 3 dimensionalcolor-coded representation. This technique would be most useful when afree-hand tracking system is used for the transducer.

In the method of the invention, the same concept of image registrationand image integration could be extended to modify the real-time USimages. Segmenting the critical structures from the 3D MR data (i.e.anatomical landmarks, contrast-enhanced lesion), and knowing theposition of the transducer relative to the MR data by way of a trackingsystem, the two image modalities could be integrated into one image.This technique does not require the lesion to appear in the US image.Rather the MR image of the lesion is identified as the target and issuperimposed on the US image. The radiologist could simply adjust thetransducer until the superimposed lesion appears in the US image, andguide a needle to that point at a trajectory determined using knowledgeof the transducer position. Similarly, the image may include asuperimposed marker representing a position-tracked device to assist inits visualization. Image fusion in this manner will also permit aquantitative measure of the accuracy with which the images have beencombined. A measure of how well the MR and US modalities are registeredcan be obtained by performing a cross correlation calculation at anytime. The radiologist can ensure that the registration is accuratebefore proceeding with the intervention.

In the method of the invention, the integration of 3-D MRI and 2-D USinformation and the overlay of segmented data (data which has beenprocessed to highlight anatomical features), needle position and USimage plane orientation enables real-time tracking of the needleposition and US beam path to facilitate real-time guidance of a devicetowards a target by ensuring they are co-aligned throughout theimaging/intervention procedure.

There is no known Prior Art presenting a system that incorporates thesetechnologies so as to provide an MRI/US combined approach to performintervention, or imaging procedures on MRI detected targets in non-rigidregions of the body that are required to be constrained to reduce errorsassociated with motion and deformations. The physical and mechanicalrestrictions associated with such an invention have been presented asaspects of the invention thus far.

Image Error Correction

The present invention also provides for integration of MR and US data,whereby information from one modality can be used to correct errorsassociated with the other modality.

Correction for US Positional Errors

Another aspect of the invention provides image integration techniques,whereby MRI data can be used to correct for errors in the US data set.It is well known that the location of features in a US image isdetermined using known values for the average speed of sound in tissue.However, fat and fibrous tissues are known to exhibit speeds of soundthat differ by 5-10%. In routine US images, a fixed speed of sound isassumed to determine location. This is an approximation and will resultin positional errors in the co-registration of the MR and US data sets.For example, if the space between the skin surface and the lesion iscomposed of purely fat and represents a thickness of ˜3 cm, then thelocation of the lesion in the US image would be in error byapproximately 1.5-3 mm and as such the MRI and US images would not beaccurately co-registered. In most applications of US imaging, this isnot a limitation, as relative position is often all that is required. Inthe method of this invention, absolute position in terms of an MRIcoordinate frame is what is required. In practical terms, the maineffect of the assumption of constant US speed-of-sound will be todistort the image in the direction parallel to the sound propagation,causing the image to be either compressed or expanded depending on theassumed speed of sound. However, refraction together with the fact thateach point in the image is formed by multiple RF measurements from eachelement in a typical US transducer can lead to lateral distortions aswell. This will be evident on the US image as spatial errors or regionsof misalignment as one attempts to overlay the US and MRI image. Inorder to overcome these distortions corrections for the actualspeed-of-sound for each transducer element must be made reflecting theactual tissues through which the US field propagates. Two possibleapproaches can be taken to overcome this limitation.

An approach is to attempt to correct for speed of sound variations bycombining the MRI and US data. This can be achieved in an interactivefashion by repeatedly correcting the US data on the basis of knowledgeof the tissue composition from the MRI data. In its most simple form,the MRI data can be used to make a first order correction of US positionby estimating the amount of fat and fibroglandular tissue through whicheach US measurement is made. We note that standard T1-weighted MRIimages render fat and fibroglandular tissues with very different signalintensities. Typically, fat appears with a high signal level (bright) asa result of a short spin-lattice (T1) time constant while fibroglandulartissues with longer T1 times, exhibit a lower signal and are seen as adark region on the image. One this basis of this contrast between thesetwo tissues, it is straightforward to segment the varying regions of theMRI data from which to calculate the distant of US propagation (andspeed) for both fat and fibroglandular tissue. As the location of the UStransducer has been positioned over the tissue on the basis ofmeasurements from the MRI image, we know the position of the UStransducer in the MRI imaging field to first order. From this thecorresponding paths of the US field for each US transducer element canthen be determined for each point within the US image. By referring tothe same point on the MRI data the path length of the fat andfibroglandular tissue can then be estimated and the corresponding speedof sound variations for that location and US transducer element can bedetermined. This can then be used to scale the all the US RF data to thevarying speed of sound within the tissue. The corrected RF data can thenbe combined to form the US image and create a corrected US image. Thiscorrected image will represent a first order correction to align the USand MRI data. When attempting to overlay the US and MRI images, theboundaries of well-defined anatomical structures, such as interfacesbetween fat and fibroglandular tissue, should be better coregistered.

As a result of this operation, each point in the corrected US image willnow be closer to its true location within the US image. This sameprocess could be repeated in an interactive or interative manner witheach successive iteration moving the points in the US image to graduallymigrate to their true corresponding location on the MRI data.

The discussion above, presumes that the geometry of MRI data isgeometrically accurate; however, it is known that various factors willmake the MRI image also exhibit spatial distortions. The mostsignificant of these are positional errors arising from magnetic fieldgradient non-linearities. Most manufacturers of MRI equipment attempt toprovide some form of correction for these gradient non-linearities onthe basis of pre-determined measurements of the gradient spatialperformance over the 3D imaging volume. In order for the segmentationscheme outlined above to be most effective, correction of MRI data isneeded.

An alternative approach to this problem is to use image co-registrationmethods to map the US data to the MRI data. A number of co-registrationmethods exist which transform the location of point with one image tobest match its location in another by satisfy varying metrics of imagesimilarity such as mutual information (Hill D L, Batchelor P G, HoldenM, Hawkes D J Medical image registration Phys Med Biol. 2001 Mar;46(3):R1-45.). With these techniques it would be possible to correct forsubtle changes arising from variations in the speed of sound in the USimages and match them to MRI images. As such, lesions which are expectedto appear on the US images can be determined uniquely from MR image. Inaddition, we could use the calculated deformation field to calculate thespeed of sound variations that would be needed to generate thisdeformation in an iterative manner similar to that described above. Assuch, the MRI data will be used to constantly update the US data inreal-time to provide accurate co-registration of the two data sets.

Defining the MR Image Plane to Track US Transducer Motions

A further aspect of this invention uses motions detected with US dataduring an intervention to modify the MR image, reflecting the new tissuegeometry. The MRI image would appear to be updated in a real-timemanner, without necessitating acquisition of new images in the MRmagnet. In the method of the invention, the entire post-MRI imagingoperation could be done outside of the magnet room by detaching thetransport stretcher from the magnet and rolling the patient out of themagnet's field. This would reduce the amount of time needed for MRmagnet access but ensure that meaningful use of the MR images would bemade during an intervention. Further embodiments include gathering 3D USdata (rather than the normal 2D images) during intervention to monitortissue and device motions. Another embodiment involves measuring theorientation of the needle from an external tracking system to overlaythis estimate of device orientation on the image data. This would serveto corroborate the device orientation with that visible on the US image,helpful when the device position is unclear in the US image.Furthermore, US imaging serves to reduce the need for further MRI.

As mentioned previously, Cormeau et al, 2000, presented a system thatintegrates US and MRI data registered using fiducial points and withprobes positioned and tracked using an optical tracking system. Thisembodiment has been specifically developed for brain applications anddoes not translate to breast applications for reasons previouslymentioned. Tissue shift correction techniques presented by Cormeau usinginformation from both modalities can be translated to the breastapplication. The current invention differs in that a well-immobilizedbreast with US imaging access provided through multiple access points(medial and lateral) enables high quality US imaging (shortest distanceimaging to the target) to be performed without gross tissue motionassociated with craniotomy associated with neurological procedures. Thecurrent invention also considers the nature of imaging errors associatedwith mis-registration errors not considered by Cormeau.

ADDITIONAL EXAMPLES OF CLINICAL APPLICATIONS OF THE INVENTION Example 9Hybrid MR/US Imaging

The simplest implementation of hybrid imaging involves the detection ofa lesion using MRI, followed by positioning of an US transducer, suchthat the lesion appears in the center of the US field of view at acalculated position, as illustrated in the flowchart shown in FIG. 28.

The breast of interest would be compressed between two acousticallytransparent compression plates. Attached to these compression plateswould be an array of coils for MR imaging. The lesion would be detectedusing MR imaging techniques and other MR imaging techniques may be usedto identify features of the breast that would be visible using US. Thiswould serve to provide features common to both imaging modalities (e.g.T2-weighted MR imaging is appropriate for imaging cysts, T1-weighted forfat-fibroglandular interfaces). The position of the target lesion andthe fiducial markers as seen on the MR image would be entered into acomputer program which determines the appropriate USH co-ordinates suchthat the lesion will appear in the US image. The ability to image frommedial or lateral sides of the breast without prior knowledge of thelesion position ensures optimal images may be obtained from the sideclosest to the lesion. After finding the lesion under MRI, the patientis transported from the MR imaging system while still immobilized on thepatient stretcher, away from the magnet's field. At this point the MRimager is free to be used for another patient. The MR imaging coils arethen removed from the compression plates and the mechanical, or freehandUS position tracking system may be attached. The transducer can thenaligned with the lesion as indicated by the MR image. The lesion ofinterest should appear at the center of the US image, at a calculateddepth from the surface of the imaging face. Lesions can then be freelyexamined using a variety of US techniques.

In some cases, the lesion may be difficult to visualize in the US image,or the position prescribed for the US transducer may be in error forvarious reasons. In these cases, additional techniques can be appliedwith some increase of complexity. The techniques of MR/US imagefusion/integration and image correction may provide the radiologist withtools to aid in identifying the lesion and provide more accurateregistration between the images. Freehand transducer positioningprovides a means of visualizing the lesion in three dimensions byimaging it through different planes. One important technique involvesthe identification of common features found in MR and US images in orderto confidently identify the lesion.

In FIGS. 20 and 21, various MR/US Hybrid biopsy configurations areshown. In a lateral biopsy approach in FIGS. 20 a, b, c and d, a breast458 (for example) is compressed between two sterile, US permeable plates451. Imaging and intervention occur from the same side. FIG. 21 a, b, cand d are essentially the same configuration as FIG. 20, with a medialbiopsy approach selected. FIG. 20 b is a configuration with onefenestrated plate and one US permeable plate. Needle approach is fromthe opposite side from US imaging. FIG. 21 b is the same configurationas FIG. 20 b with a needle guide plug used to deliver needle. FIG. 20 cuses a plate with larger fenestrations which can be used to incorporatea transducer and needle for same side imaging and intervention. FIG. 21c is the same configuration as FIG. 20 c showing a view from a lateralside. FIG. 20 d shows an alternative transducer and needle deliverythrough the same side using a positioning stage. FIG. 21 d is anotherembodiment with 2-point needle positioning system on opposite side to USimaging.

A radiologist may use the information in the registered MR/US images todetermine the pathological status of the tissue in question. Forexample, a breast lesion may be defined as malignant or benign based onwell-understood features visible in the US image such as lesionmorphology, or blood flow characteristics. The radiologist may alsoidentify unique features of the lesion such as its appearance, size orlocation relative to anatomical landmarks in order that it may beidentified on a subsequent retrospective US-guided biopsy.

Example 10 Hybrid Biopsy

A preferred embodiment of the hybrid imaging technique disclosed by thepresent invention is its application in acquiring biopsy samples oflesions that are detected using MRI and cannot be biopsiedretrospectively through any other traditional means (e.g. if the lesionis not identifiable on the basis of US alone). Biopsy would then beperformed making use of hybrid imaging.

According to this invention, the procedure for hybrid biopsy is similarto that for hybrid imaging, but in addition a biopsy needle would beintroduced into the breast with US verification imaging. The generalprocedure is illustrated in the flowchart shown in FIG. 29.

This procedure requires the same apparatus as the hybrid imagingprocedure, except the compression plates used would differ and a needleguidance strategy and apparatus may be incorporated into the procedureas required. Various setups for the procedure are shown in FIG. 21 andFIG. 22. In all cases shown, the contralateral breast is compressedagainst the chest wall. However both breasts can be constrained betweenplates and biopsied if both breasts extend into the interventionalvolume below the patient support. This would limit the biopsy approachto a lateral approach on either breast.

In each of the configurations shown in FIGS. 20 and 21 a, b, c and d,the compression plates have electrical connections for MR imaging coils(connections not shown). MR imaging is performed to detect the tumor andbreast's features along with fiducial markers. The relative positionsfiducial marker and target lesion are used to determine appropriate USHaxis positions, bringing the US imaging plane through the lesion. Afterthis point the biopsy techniques employed differ according to theparticular strategy used.

According to one aspect of the invention, the breast of interest wouldbe compressed between two US-transparent compression plates, as shown inFIGS. 20 and 21 a, b, c and d. These plates would be prepared with asterilized membrane, as well as requiring that the coupling gel betweenthe membrane and the sterilized breast would be sterile. Such acompression system presented as a sterile surface and an acousticallytransparent member has not been presented in any Prior Art and isfundamental to the success of such a technique. After lesion detection,an appropriate US transducer position would be determined such that thefollowing criteria are satisfied: i) the shortest imaging distance isselected (either medial or lateral approach) ii) transducer positionprovides clearance for biopsy needle entry and avoidance of biopsysystem components, iii) the transducer orientation is optimized forlesion visualization. The transducer may be delivered to the appropriateorientation using the USH device and/or a free-hand tracking technique.The transducer positioning technique that provides the greatest accessto the breast for needle positioning is preferred. The access providedby the system to the breast further enables the option of freehand USimaging with one hand from one side of the breast, and needlepositioning from the other side of the breast. This configuration maynot be optimal from the standpoint of the radiologist's dexterity,however this approach option is provided in one embodiment of theinvention. The approach shown in FIGS. 20 and 21 with needle deliveryand US imaging from the lateral approach would be used when the lesionis positioned in the lateral region of the breast. The approach shownwith needle delivery and US imaging from the medial side of the breastwould be used when the lesion is located in the medial region. In allcases the lesion would first be identified on the US images using thetechniques previously presented. When identified, the transducer wouldbe positioned so as to provide room for needle entry, or positioned soas to monitor the needle as it is introduced into the breast. In caseswhere the lesion is not obvious, addition of MR/US fusion strategiescould be applied. Further application of needle tracking andpresentation on the fused image set would also be of great benefit inthis application as well as all other hybrid imaging strategies toassist in needle identification.

In another embodiment of the invention, the breast would be compressedbetween one US-transparent compression plate and one fenestrated plateon the opposite side, as illustrated in FIGS. 20 and 21. It is customaryto select the shortest biopsy trajectory in order to minimize breasttrauma. In this configuration the hybrid biopsy concept can be performedin a variety of ways, each using the basic concept of US transducerpositioning and either free-hand needle delivery or stereotactic needledelivery. These techniques are described below, in accordance with theinvention.

1) Stereotactic US Transducer Delivery, Freehand Needle Delivery

The lesion and fiducial are located using MRI. The patient/biopsyapparatus are removed from the MR imager and apparatus prepared for USimaging and needle intervention. The US transducer would be deliveredaccording to MR image coordinates, and the lesion is identified on theUS images. The US transducer may be repositioned to aid in identifyingthe lesion. On the opposite side of the breast, the appropriate apertureof the fenestrated plate is selected for needle entry using knowledge ofthe lesion's position. The needle would be introduced into the breastand its trajectory modified based on the US images. A biopsy samplewould then be acquired the guide needle is in the appropriate position.Multiple samples may be acquired using, offsetting the biopsy needle'sposition for each. Multiple lesions may also be examined in the samebreast, in the same procedure using this strategy.

2) Stereotactic US Transducer Delivery, Stereotactic Needle Delivery (NoMR Verification)

This embodiment of the invention is similar to the one proposed above,differing only in the extent to which the MRI data is used to helpposition the needle and transducer. The lesion and fiducial markerswould be identified using MRI. These positions would then be enteredinto a program that would determine the appropriate needle deliverytrajectory based on the shortest distance to the lesion, or restrictedto a fenestration selected by the radiologist. Based on the needleorientation, the transducer orientation would be calculated such thatthe needle would appear in the plane of the US transducer as it isintroduced into the breast. The patient would then be removed from themagnet bore, and prepared for US imaging. The US transducer would bepositioned according to the above calculation and the lesion identifiedon the US image. The needle would be introduced into the opposite sideof the breast through the needle guide plug and its trajectory modifiedbased on the MR or US verification images. The guide plug may beloosened and the needle trajectory modified as required. Multiplesamples may be acquired.

3) Stereotactic US Transducer Positioning, Stereotactic Needle Delivery(MR Verification)

In a third embodiment of the invention used with this plateconfiguration, MRI is used to detect and to validate the needle positionbefore the US imaging procedure is performed. The lesion and fiducialmarkers would be located using MRI. The appropriate needle deliveryorientation to the lesion would be calculated based on the MR data suchthat the shortest distance to the lesion would be selected (alsoconsidering the positioning of the US transducer and limitations of theapparatus in the immediate area). An MRI compatible needle would then bedelivered to the lesion at the desired orientation using the angledneedle guide plug presented previously. MR imaging would then be used tovalidate needle position. The needle position may be modified asrequired with additional MR imaging. The patient would be removed fromthe MR magnet room and the apparatus setup for US imaging. The UStransducer would be positioned to an appropriate orientation to allowthe needle and lesion to be imaged. The needle trajectory may bemodified as required by unlocking the needle guide plug before thebiopsy sample is acquired.

The examples presented above are all embodiments of the invention. Eachembodiment has certain advantages. For instance, one embodiment requiresthe operator to deliver the needle by free-hand guidance. This strategyis a fast technique requiring no needle guidance apparatus, however itrelies on the radiologist's dexterity. A second embodiment (employingstereotactic needle delivery outside the MR magnet) requires moreapparatus; however it provides a fast means of needle delivery and hasfewer demands for accuracy on the radiologist. The third embodiment,which requires MR-verification of the needle before US imaging/needleverification is a longer procedure, however it does provide anadditional MR image as verification. The last embodiment is limited inthat the patient must remain in the prone position with the biopsyneedle in the breast for a longer period of time.

In another aspect of the invention, fenestrated plates that haveopenings large enough to accept either the front end of an UStransducer, or a biopsy needle, or a needle guide plug, are positionedas medial and lateral compression plates. This configuration enablesimaging and intervention from either medial or lateral approaches. Thisconfiguration further enables free-hand biopsy, or stereotactic needledelivery techniques. The design of the plates should be such that theopenings are large enough to allow the transducer access to the breast,however not large enough that a large volume of breast tissue bulgesthrough the openings. According to the invention, an acousticallypermeable membrane is pulled taut and positioned between the breast andthe fenestrated plate can be used to constrain the breast in thisimplementation. This has the benefit of good breast immobilization, goodaccess for US imaging, and provides a frame to which needle positioningplugs may be attached.

In yet another aspect of the invention, two different needle positioningstrategies are applied. The implementation of the two-point needlepositioning device corresponding to the US transparent membrane is shownin FIGS. 20 d and 21 d. This can be used on either the same side of thebreast as the US transducer or, as shown here, on the opposite side. InFIG. 21 d we see an additional needle guide attached to the UStransducer positioning device.

In all of the above hybrid biopsy strategies, the lesion may not bevisible to US. In some cases the lesion may not be identifiable due topoor US image contrast. In these cases, the operator may choose tobiopsy the tissue identified by the MR images. A biopsy may be acquiredmore confidently if image fusion techniques are employed. According tothe invention, other imaging techniques, including US Doppler, Harmonicand US micro-bubble contrast, may be used to enhance the quality of theimages acquired. In the method of the invention, all biopsy strategiescan be extended to multiple lesions in a single procedure. None of thesetechniques have been described in detail in previous Prior Art. Anarticle by Plewes 2001, IEEE, presents a simplistic form of thetechnique where US and needle delivery is performed from opposing sideswith the shortest distance taken to be from the needle insertion tolesion center, however none of the enabling aspects of the inventionwere presented.

Example 11 Hybrid Marker Placement

According to the invention, using a technique similar to MR-guidedbiopsy of the breast, a small position-marking device may be implantedin the breast in conjunction with a biopsy or wire localizationprocedure. Any of the previously presented hybrid biopsy techniquescould be applied as needed. Marker placement using MR-guidance alonewould require multiple image acquisitions to verify position prior toeach marker placement. Lesions only visible under contrast enhancementcannot be imaged repeatedly with MRI during the same procedure. Guidanceof marker placement devices using US is not restricted by time-limitedlesion contrast enhancement, and does not require long periods ofexpensive MR magnet time. US cannot always be relied upon to visualize alesion's exact location or extent, but can be used to track tissuemotions during the intervention. In this technique, MR images arereformatted to reflect the changing image plane of a US transducer, andmodified in real-time to indicate tissue distortion detected with US.This confers the ability to image in real-time with ultrasound, but tostill visualize lesions to the extent possible with MRI.

The marker placement device's position would be known from both the USdata and from a separate position tracking system. A representation ofthe device's location would be overlaid on the reformatted MR imagedescribed above. Markers may then be positioned relative to a lesion asit appears on MRI, but whose morphology is being updated based on USmonitoring.

According to the invention, these markers do not have to be made of MRcompatible materials. In one embodiment, they are constructed ofmaterials and geometries that are easily identified on US images (highlyUS reflective scattering). In another embodiment, these markers are madeof MR compatible materials so that their positions may be verifiedrelative to the lesion enhancement pattern on subsequent MR imagingprocedures (e.g. supine MR imaging may be preferable, in order to locatemarkers with the patient in the position used for surgery). Thisprocedure is demonstrated in FIG. 22 and FIG. 23 and in the flowchartshown in FIG. 30. Marker placement under mammography, ultrasound and MRIhave been presented in recent years, however multiple marker placement,and MR/US combined marker placement have not been presented in the priorart. FIG. 22 shows the positioning of multiple clips 500 at a lesion 502in a breast 458 by devices 452 guided by transducer 450 from a medialperspective. FIG. 23 shows an image of the devices inserting the markersfrom the physician's point of view.

FIG. 24 a shows that hybrid needle 542 (e.g., tissue ablation probe suchas a cryotherapy probe) may be delivered to a lesion 502 in a breast458, with delivery made in multiple positions based on MRI imaging. InFIG. 24 b, it is indicated that therapy can be monitored with US and/orcorresponding MR data as a US image 545 or reformatted MRI image 544. Alesion 502 may be segmented from the MRI data through various means,with probe position 542 and tissue architecture demonstrated in thereformatted MR image 544. The corresponding features may be present inthe corresponding US image as an US visible lesion 545 with or withoutfused MRI data to assist in validation of lesion position and/or probeposition.

Example 12 Hybrid Monitoring of Therapy Delivery

According to the invention, this system can be used to accommodate avariety of tissue investigation or ablation devices, such as invasiveultrasound tissue ablation devices, RF heating devices, cryotherapysystems, local delivery of chemotherapeutic agents, optical ablation(lasers), optical photodynamic systems, or any other tissue destructiontechnique. Monitoring of these therapies may be performed using theposition-tracked US transducer with imaging techniques such as standardgrayscale imaging, Doppler imaging to characterize in blood flow, ormeasurement of temperature as a function of changes in the speed ofsound and attenuation properties. Grayscale US imaging has been shown tobe a reliable technique to monitor delivery of cryoablative therapy, asthe ice formed in the tissue is readily detected as a highlyUS-reflective surface. The utility of US as the monitoring and deviceguidance technique is to provide more accurate device placement, as wellas limit the amount of expensive MR imaging time required to monitorlong treatments (thermal ablation of tumors may be up to ninety minutesin duration). This procedure is demonstrated in FIGS. 24 a and b and inthe flowchart shown in FIG. 31.

Minimally invasive tissue ablation techniques have been presented inrecent years for breast, brain prostate and liver therapy. Limited usefor breast cancer ablation has been presented. No prior art has beenpresented involving a combined MRI detection and US guidance strategyfor these therapies. MRI detection and MRI monitoring has been used forcryoablation and laser ablation of breast tumors, without US guidanceand monitoring. Differing from the presented invention is a systemdeveloped by TxSonics Inc using MRI guidance to detect tumors andmonitor therapy, and high-power US to ablate tumors. Only through amodification of the approaches taken in inventions thus far can anappropriate embodiment be realized. Only the use of US-guidance tomonitor ablation therapies can decrease the expensive MRI time requiredto perform these procedures making them more economically appropriate.

The preceding specific embodiments are illustrative of the practice ofthe present invention. It is to be understood that other embodimentsknown to those skilled in the art or disclosed herein may be employedwithout departing from the invention or the scope of the claims.

The practice of the invention as described above provides the followingsystems functions:

-   -   Technique for medial/lateral MR-guided delivery of needle to the        breast using straight or angled needle trajectories.    -   Techniques for MR/US hybrid biopsy    -   Technique to co-register MR and US images        -   Reformatting of MR image to correspond to US image        -   Correction of US image for speed of sound variations        -   Correction of image co-registration errors        -   Registration of common anatomical features used to calculate            co-registration accuracy    -   Delivery of a variety of needle gauge sizes as well as various        minimally invasive treatment devices.    -   Positioning of multiple marking coils into the breast to define        boundaries of lesions through a single incision.

According to the invention, the following functions are provided withminimal reconfiguration of the apparatus:

-   -   1) High quality breast images in bilateral screening and        unilateral follow-up examinations using various MR coil        configurations can be used for both procedures, and comprising        an optimal breast compression strategy as well as optimizing        access to the breast by the MR technician;    -   2) MR-guided localization, including medial or lateral biopsy,        without prior knowledge of lesion location;    -   3) MR-guided multiple biopsy, including medial or lateral        biopsy, with or without angulated needle approach;    -   4) MR-guided marker placement for improved surgical excision,        under MR guidance, wherein a marker is positioned at the edges        of the lesion as defined by MRI. The procedure would be similar        to the MRI-guided biopsy procedure, however, a marker would be        placed into the breast rather removing a sample of tissue. This        may be conducted in conjunction with MR-guided biopsy, in        conjunction with MR-guided needle localization.    -   5) MR-guided positioning of devices other than biopsy needles,        including tissue investigation or ablation devices, such as        invasive ultrasound tissue ablation devices, RF-heating        applicators, cryoablative systems, miniature imaging coils, or        optical photodynamic systems. According to the invention,        monitoring of these devices may be done using the MR system to        measure heating or cooling patterns during therapy. In the case        of the optical systems, treatment region may be determined using        other techniques (i.e. T2-weighted contrast sequences).    -   6) MR-US fusion imaging, wherein real-time US data can be used        to position a device accurately into the lesion. This may be        done using US exclusively when the lesion is visible on the US        image, or using a combination of the MRI and US data fused using        a variety of techniques. This strategy involves detecting the        lesion using MRI, then removing the patient from the MR magnet        room to perform US imaging. According to the invention, US        imaging could involve a number of procedures        -   a. US imaging—simple use of the US so as to identify the            lesion and determine its malignancy status. Identification            of the lesion in this manner could also act to provide            lesion location and US properties with which the lesion may            be identified for subsequent US-guided biopsy with the            patient removed from the biopsy apparatus. Knowledge of the            US features of the lesion could lead to easy identification            of the lesion in a follow-up US examination. In cases where            the lesion is difficult to identify in the US image, the            option to view the lesion as a fusion image may assist in            visualization.        -   b. Hybrid biopsy—this technique involves the use of the            interventional US imaging membrane. This procedure requires            stereotactic positioning of the US transducer in conjunction            with free-hand delivery of the biopsy needle. This may be            augmented by the use of a fused MR/US data set, and with or            without the use of position-tracked US transducer and biopsy            needle. Markers can be superimposed onto the MR/US fused            dataset in such a way that the needle is easily identified            on the MR/US fused image set, and in a way that the            presented MR/US image updates to reflect the position of the            US transducer.        -   c. Hybrid marker placement. Based on the procedure above,            except that a MR and US-visible marker is implanted in the            breast. This results in more accurate marker placement and            reduces the amount of time spend in the MR-magnet room.        -   d. Hybrid treatment. The hybrid device delivery technique            may also be used to deliver devices other than biopsy            needles and marker placement devices such as tissue            investigation or ablation devices.

In this case it is advantageous to monitor the therapy using US.

This offers the ability to improve the accuracy of the delivery andreduces the amount of time required for MR imaging. Again, this can beused with either the combined MR/US images, or using only the US imagesif the lesion can be confidently identified on the US image. The use ofthe fused MR/US data is beneficial when MRI provides better definitionof tumor boundaries.

According to the invention, numerous techniques and methods can be usedto enable the practice of the various embodiments of the invention, asillustrated by the following specific examples:

Stereotactic positioning of needle/US transducer based on MRcoordinates:

-   -   Specification to deliver needle in straight (e.g.        medial-lateral) orientation.    -   Specification of angulated needle delivery:        -   ability to select shortest needle paths, or desired needle            angle.        -   ability to eliminate occluded areas behind fenestrated            constraint plates        -   ability to identify guide needle position on MR images to            ensure that the chest wall will not be punctured during            biopsy acquisition    -   Specification of exact US transducer orientation and position,        with transducer mounted horizontally or vertically, under        various constraints (minimal distance, selected orientation,        etc.)

US transducer position tracking co-registered with breast frame ofreference:

-   -   Ability to determine transducer frame of reference relative to        breast frame of reference. This enables the device plane to        correspond with the MRI coordinates.    -   Uses of tracking position of US imaging plane:        -   Calculating corresponding plane from 3D MR data set            (creating virtual US image composed of reformatted MR data)            will correspond to US image position and orientation.        -   distance to lesion through-plane will be determined and            shown relative to virtual US image.        -   position of lesion center on US image will be identified.        -   MR data can be combined with the virtual US image to form a            fused MR/US image.        -   Segmentation of MR lesion from contrast-enhanced data will            be superimposed on the virtual US image to form a composite            image.        -   Other auditory, tactile and visual cues may be used to guide            free-hand US transducer movement, enabling the user to            operate the system with or without a view of the US image.    -   Means of displaying position information about an interventional        device:        -   a device's position may be tracked and an indication of its            position superimposed over an acquired image (i.e. tracking            a biopsy needle and superimposing an image of the device on            the co-registered MR, US, or fused MR/US images.    -   Integration of images and position tracking data to validate US        and MR image co-registration:        -   use of landmarks identified on US and MR images to confirm            that the MR image is aligned with the US image        -   use of image processing techniques and image acquisition            techniques to better identify common landmarks on both            imaging modalities. (i.e. breast parachymal patterns,            vessels, cysts).        -   Method to quantify the similarity of two modalities. Means            of presenting the result to the operator.        -   Means of correcting the registration between the two            modalities:            -   Speed of sound correction.                -   Use the MRI data to determine composition of the                    breast, use known speed of sound values for the                    appropriate tissues and correct the US image.            -   Gradient warp shifts.                -   Correct for large errors due to gradient warp in the                    MR imaging system.            -   Position or registration error due to patient motion.                -   Relies on operator identification of similar                    features on both modalities. Once selected, the user                    may displace one image set to match the other, or                    may use automated image processing algorithms for                    this purpose.

As discussed herein, the benefits of the invention include, but are notlimited to:

-   -   System that can be used for breast imaging and multiple        intervention functions.    -   Improved access to the entire breast volume for imaging and        intervention.    -   Improved breast immobilization through full compression of        breast (including volume near chest wall).    -   Improved breast compression technique for operator ease of use.    -   Improved probe delivery using MRI guidance:    -   More accurate probe delivery—angled delivery provided greater        access.    -   Multiple target sampling through a single incision point.    -   Flexibility in the selection of biopsy approach (medial or        lateral) to minimize trauma to the breast    -   Real-time US guided probe delivery through hybrid technique.    -   US guided sampling in the fringe field or even in another        procedure room.    -   Flexibility in the selection of biopsy approach (medial or        lateral) to minimize trauma to the breast and distance of breast        tissue traversed for US imaging.    -   Ability to obtain many tissue samples through one small skin        incision.    -   Ability to use standard interventional devices under US        guidance, not limited to equipment that is MR compatible, thus        reducing disposable equipment costs and permitting use of        superior, non-MR-compatible devices.    -   Separation of MR imaging and biopsy procedure into two stages        that can be performed in different locations using one dedicated        transport stretcher, thus freeing the MR facility and its own        dedicated patient transport stretcher for the next patient.

The foregoing description of the invention is not intended to describeevery object, feature, advantage, and implementation of the presentinvention. While the description of the embodiments of the invention isfocused on applications for breast imaging, it will be understood bythose skilled in the art that the present invention has utility toapplications elsewhere in the body. The primary differences would relateessentially to the geometry of the frames, which would hold the needleentry plate and the US plate.

All patents and printed publications referenced herein are herebyincorporated by reference into the specification hereof, each in itsrespective entirety.

1-62. (canceled)
 63. A method performed on an apparatus to monitor andoptimize the placement of interventional medical devices in humantissues of a patient comprising (a) imaging and positioning saidinterventional medical devices within said tissues on the basis of 3D MRimaging data; (b) co-registering MR images and ultrasound images basedon measurements of fiducial markers obtained during said MR imagingprocedure; (c) positioning the patient on the apparatus and enablingunrestricted access to points on the surface and within the volume ofsaid tissues; (d) the apparatus comprising a patient support structure,with associated patient transport stretcher that enables imaging andpositioning of said interventional devices within said tissues.
 64. Themethod of claim 63, wherein said tissues are positioned in a prescribedconfiguration with known reference points within said tissues, thispositioning allowing MRI to be used outside the MR imager.
 65. Themethod of claim 64, wherein said reference points within said tissueminimize MR imaging time and facilitate the guidance of MR-incompatibledevices with MR data outside the imager.
 66. The method of claim 63,wherein ultrasound transducers are guided to prescribed imaging planesto simplify co-registration of said imaging data, thereby permittingaccurate guidance of multiple said interventional devices to multipletargets within said tissues through a single surgical incision.
 67. Anapparatus used to assist in monitoring and optimizing the placement ofinterventional medical devices in human breast tissues comprising apatient support structure with an associated patient transportstretcher, the structure and the stretcher enabling imaging andpositioning of the interventional devices within human breast tissues byproviding breast support without restricting interventional access tothe breast tissues, the apparatus enabling access to points on thesurface and within the volume of said breast.
 68. The apparatus of claim67 wherein breast compressing plates enabling bilateral imaging withboth breasts are provided on the apparatus.
 69. The apparatus of claim67 wherein said apparatus allows access to areas near the chest wallfrom both lateral and medial approaches with only minimally interferingsupport structures.
 70. The apparatus of claim 67, wherein said patienttransport stretcher additionally provides (a) a removable bridgeproviding a large volume in which to position said devices and gainaccess to the breast, (b) a means of replacing said bridge such thatcontinuous patient support is provided when said patient is moved in andout of the bore of the imager; (c) lighting devices positioned toprovide illumination from both medial and lateral access directions, (d)mirrors positioned such that an operator may easily see the nipple ofthe breast when positioning the patient and applying compression to thebreast; (e) fluid collection device positioned under the breastundergoing imaging which covers medial and lateral aspects of saidbreast and moves with the patient into and out of the imager.
 71. Theapparatus of claim 67 wherein compression plates comprising multiplelocking supports running along linear guides can be moved inmedial/lateral directions, locked independently in any position, andintroduced and removed from the apparatus with the patient lying on thesupport structure.
 72. The apparatus of claim 71 wherein modular platelocking supports fix said compression plates for MR imaging.
 73. Theapparatus of claim 72 wherein said modular plate locking supports andsaid compression plates arte provided with single or multiple coils forMR imaging
 74. The apparatus of claim 72 wherein said modular platelocking supports and said compression plates are provided with afenestrated plate for MR interventions, Ultrasound imaging, andUltrasound interventions.
 75. The apparatus of claim 68 wherein saidcompression plates may be moved vertically, anterior-posterior to thepatient, and locked relative to the compression frames to compress thebreast near the chest wall.
 76. The apparatus of claim 75 wherein saidcompression plates additionally provide fiducial markers asintra-modality reference points,
 77. The apparatus of claim 75 whereinsaid compression plates also provide attachment points for imagingcoils, device delivery devices, fiducial marker plate arrangements, andfenestrated immobilization plates.
 78. The apparatus of claim 72 whereinsaid compression plates compress and immobilize the breast andincorporate an MR imaging coil or coil array in close contact with thebreast.
 79. The apparatus of claim 78 wherein said compression platesincorporate fiducial markers and an array of apertures providing accessto the breast for interventions.
 80. The apparatus of claim 79 whereinfenestrations in said compression plates are keyed to accept deviceguide plugs in only one orientation.
 81. The apparatus of claim 80wherein said fenestrations are packed in a hexagonal orientation. 82.The apparatus of claim 79 wherein said compression plate may be moved inthe anterior/posterior direction relative to the patient.
 83. Theapparatus of claim 79 wherein said compression plate may be moved in asuperior/inferior direction relative to the patient.
 84. The apparatusof claim 79 wherein said compression plates consist of a framesupporting a membrane, allowing position adjustment of an attachedfenestrated plate without disturbing the position of the breast.
 85. Theapparatus of claim 84 wherein the opening of said frame in saidcompression plates is large enough to provide access to the entirebreast volume.
 86. The apparatus of claim 84 wherein said membrane issterile and can be replaced for each procedure.
 87. The apparatus ofclaim 84 wherein said fenestrated frame can be locked into positionrelative to compression plate in various orientations, such that eachorientation permits interventional access to a different volume of thebreast.
 88. The apparatus of claim 84 wherein said fenestrated plate hasfenestrations positioned such that shifting said frame by thefenestration separation distance ensures improved access to breastvolume.
 89. The apparatus of claim 79 wherein said frame provides a setof attachment points for an ultrasound positioning system, fiducialmarkers and an adjustable fenestrated plate.
 90. The apparatus of claim79 wherein said frame supports a membrane permeable to ultrasound. 91.The apparatus of claim 90 wherein said membrane has an acousticimpedance matched to tissue being imaged.
 92. The apparatus of claim 88wherein said fenestrated plate is designed to allow an ultrasoundtransducer to come into contact with an ultrasound-permeable membrane.93. The apparatus of claim 92 wherein said fenestrated plate containsapertures in which is inserted a set of device delivery guide plugs. 94.The apparatus of claim 80 wherein straight needle guide plugs arepositioned into said keyed fenestrations of said interventionalcompression plates.
 95. The apparatus of claim 80 wherein the needleguide plugs are positioned in said fenestrations of said interventionalcompression plates.
 96. The apparatus of claim 94 wherein said guideplugs accommodate various needle gauges and can be adjusted through anangular range.
 97. The apparatus of claim 94 wherein gimbaled guideplugs are constructed to allow angulation of the needle during insertioninto the mounting frame or plate in only one orientation to preservecorrect needle orientation relative to anatomy.
 98. The apparatus ofclaim 97 wherein a goniometer accepts said gimbaled guide plug andpositions the gimbal to the correct angular orientation for needleplacement.
 99. The apparatus of claim 98 wherein said goniometer has adetachable guide plug disc which can be removed for sterilization. 100.The apparatus of claim 98 wherein said goniometer also has a detachableneedle guide extender which fits outside the needle guide and can bedetached for sterilization.
 101. The apparatus of claim 5 wherein anultrasound transducer positioning device is configured on the patientsupport structure such that at least one of the following features isprovided: a 5 or 6 degree of freedom positioning device is attached at aknown position relative to fiducial reference markers; a positioningsystem is provided that enables a large range of transducer positions ina limited space; a positioning system provides access to the chest wallby positioning the transducer on top of a turret; a positioning systemis provided that enables attachment of multiple transducer nests,ensuring repeatable, accurate fixturing of different transducers; apositioning system is provided that holds a transducer in vertical andhorizontal positions relative to the axes of motion; and a positioningsystem is provided that enables the transducer face to be in contactwith the imaging surface as it is moved through vertical and horizontaldirections.
 102. The apparatus of claim 101 further comprising a needledelivery system.
 103. The method of claim 1 wherein means are providedto co-register the US images and the MRI images based on measurements offiducial markers obtained during the MR imaging procedure.
 104. Themethod of claim 103 comprising monitoring said needle orientation andposition during needle insertion.
 105. The method of claim 103comprising pre-positioning the ultrasound imaging plane to be inco-registration with the desired needle trajectory and therebymonitoring needle trajectory during needle insertion.
 106. The method ofclaim 103 comprising positioning and tracking the ultrasound imagingplane based on measurements from a free-hand tracking device.
 107. Themethod of claim 103 comprising positioning and tracking interventionaldevices based on measurements from a free-hand tracking device.
 108. Themethod of claim 105 comprising dynamically reformatting the MR images toreflect US transducer position.
 109. The method of claim 106 comprisingrepresenting the position of said interventional devices on the US andMR images as an overlay.
 110. The method of claim 104 comprisingmeasuring the changes in tissue motion arising from the needle entry bymonitoring the motion of speckle through real-time 2D/3D correlationtechnique,
 112. The method of claim 103 comprising mapping the locationof an MRI detected lesion onto the US image as an overlay.
 113. Themethod of claim 104 comprising mapping the tissue motion as measured by2D/3D-speckle tracking and to morph the MR images to reflect tissuedistortion arising from lesion motion.
 114. The system of claim 103comprising obtaining a quantitative measure of 2D/3D image registrationaccuracy using features common in both modalities, and said quantitativemeasure is used to correct for gross patient motion and misregistrationerror.
 115. An apparatus used to assist in monitoring and optimizing theplacement of interventional medical devices in human breast tissuescomprising a patient support structure carried on an associated patienttransport stretcher, the patient support structure comprising a) aforward support surface that ramps upward towards at least one openingfor positioning of breasts and then provides a more forward headsupport, b) an lower trunk support surface, and c) a structural elementconnecting a) and b), with an open area beneath the structuralconnection.
 116. The apparatus of claim 115 wherein the at least oneopening provides compression plates for the breasts that allow insertionof interventional devices into breast tissue while breasts arecompressed.
 117. The apparatus of claim 115 wherein at least part of thestructural element is retractable.
 118. The apparatus of claim 116wherein at least part of the structural element is retractable.
 119. Theapparatus of claim 116 wherein the patient support structure rolls onguides connected to the stretcher to allow extension of the patientsupport structure into a bore of an MR imager.
 120. The apparatus ofclaim 116 wherein a removable section exists between a) and b) and thatremovable section may be removed without eliminating structuralconnection between a) and b).
 121. The apparatus of claim 116 whereinfenestrations are provided in the compression plates to enable insertionof interventional medical devices into the breast tissue.
 122. Theapparatus of claim 121 wherein a gimballing support for interventionalmedical devices is present in at least one fenestration in at least onecompression plate.